diff --git a/Documentation/vm/frontswap.txt b/Documentation/vm/frontswap.txt
new file mode 100644
index 0000000..37067cf
--- /dev/null
+++ b/Documentation/vm/frontswap.txt
@@ -0,0 +1,278 @@
+Frontswap provides a "transcendent memory" interface for swap pages.
+In some environments, dramatic performance savings may be obtained because
+swapped pages are saved in RAM (or a RAM-like device) instead of a swap disk.
+
+(Note, frontswap -- and cleancache (merged at 3.0) -- are the "frontends"
+and the only necessary changes to the core kernel for transcendent memory;
+all other supporting code -- the "backends" -- is implemented as drivers.
+See the LWN.net article "Transcendent memory in a nutshell" for a detailed
+overview of frontswap and related kernel parts:
+https://lwn.net/Articles/454795/ )
+
+Frontswap is so named because it can be thought of as the opposite of
+a "backing" store for a swap device.  The storage is assumed to be
+a synchronous concurrency-safe page-oriented "pseudo-RAM device" conforming
+to the requirements of transcendent memory (such as Xen's "tmem", or
+in-kernel compressed memory, aka "zcache", or future RAM-like devices);
+this pseudo-RAM device is not directly accessible or addressable by the
+kernel and is of unknown and possibly time-varying size.  The driver
+links itself to frontswap by calling frontswap_register_ops to set the
+frontswap_ops funcs appropriately and the functions it provides must
+conform to certain policies as follows:
+
+An "init" prepares the device to receive frontswap pages associated
+with the specified swap device number (aka "type").  A "store" will
+copy the page to transcendent memory and associate it with the type and
+offset associated with the page. A "load" will copy the page, if found,
+from transcendent memory into kernel memory, but will NOT remove the page
+from from transcendent memory.  An "invalidate_page" will remove the page
+from transcendent memory and an "invalidate_area" will remove ALL pages
+associated with the swap type (e.g., like swapoff) and notify the "device"
+to refuse further stores with that swap type.
+
+Once a page is successfully stored, a matching load on the page will normally
+succeed.  So when the kernel finds itself in a situation where it needs
+to swap out a page, it first attempts to use frontswap.  If the store returns
+success, the data has been successfully saved to transcendent memory and
+a disk write and, if the data is later read back, a disk read are avoided.
+If a store returns failure, transcendent memory has rejected the data, and the
+page can be written to swap as usual.
+
+If a backend chooses, frontswap can be configured as a "writethrough
+cache" by calling frontswap_writethrough().  In this mode, the reduction
+in swap device writes is lost (and also a non-trivial performance advantage)
+in order to allow the backend to arbitrarily "reclaim" space used to
+store frontswap pages to more completely manage its memory usage.
+
+Note that if a page is stored and the page already exists in transcendent memory
+(a "duplicate" store), either the store succeeds and the data is overwritten,
+or the store fails AND the page is invalidated.  This ensures stale data may
+never be obtained from frontswap.
+
+If properly configured, monitoring of frontswap is done via debugfs in
+the /sys/kernel/debug/frontswap directory.  The effectiveness of
+frontswap can be measured (across all swap devices) with:
+
+failed_stores	- how many store attempts have failed
+loads		- how many loads were attempted (all should succeed)
+succ_stores	- how many store attempts have succeeded
+invalidates	- how many invalidates were attempted
+
+A backend implementation may provide additional metrics.
+
+FAQ
+
+1) Where's the value?
+
+When a workload starts swapping, performance falls through the floor.
+Frontswap significantly increases performance in many such workloads by
+providing a clean, dynamic interface to read and write swap pages to
+"transcendent memory" that is otherwise not directly addressable to the kernel.
+This interface is ideal when data is transformed to a different form
+and size (such as with compression) or secretly moved (as might be
+useful for write-balancing for some RAM-like devices).  Swap pages (and
+evicted page-cache pages) are a great use for this kind of slower-than-RAM-
+but-much-faster-than-disk "pseudo-RAM device" and the frontswap (and
+cleancache) interface to transcendent memory provides a nice way to read
+and write -- and indirectly "name" -- the pages.
+
+Frontswap -- and cleancache -- with a fairly small impact on the kernel,
+provides a huge amount of flexibility for more dynamic, flexible RAM
+utilization in various system configurations:
+
+In the single kernel case, aka "zcache", pages are compressed and
+stored in local memory, thus increasing the total anonymous pages
+that can be safely kept in RAM.  Zcache essentially trades off CPU
+cycles used in compression/decompression for better memory utilization.
+Benchmarks have shown little or no impact when memory pressure is
+low while providing a significant performance improvement (25%+)
+on some workloads under high memory pressure.
+
+"RAMster" builds on zcache by adding "peer-to-peer" transcendent memory
+support for clustered systems.  Frontswap pages are locally compressed
+as in zcache, but then "remotified" to another system's RAM.  This
+allows RAM to be dynamically load-balanced back-and-forth as needed,
+i.e. when system A is overcommitted, it can swap to system B, and
+vice versa.  RAMster can also be configured as a memory server so
+many servers in a cluster can swap, dynamically as needed, to a single
+server configured with a large amount of RAM... without pre-configuring
+how much of the RAM is available for each of the clients!
+
+In the virtual case, the whole point of virtualization is to statistically
+multiplex physical resources acrosst the varying demands of multiple
+virtual machines.  This is really hard to do with RAM and efforts to do
+it well with no kernel changes have essentially failed (except in some
+well-publicized special-case workloads).
+Specifically, the Xen Transcendent Memory backend allows otherwise
+"fallow" hypervisor-owned RAM to not only be "time-shared" between multiple
+virtual machines, but the pages can be compressed and deduplicated to
+optimize RAM utilization.  And when guest OS's are induced to surrender
+underutilized RAM (e.g. with "selfballooning"), sudden unexpected
+memory pressure may result in swapping; frontswap allows those pages
+to be swapped to and from hypervisor RAM (if overall host system memory
+conditions allow), thus mitigating the potentially awful performance impact
+of unplanned swapping.
+
+A KVM implementation is underway and has been RFC'ed to lkml.  And,
+using frontswap, investigation is also underway on the use of NVM as
+a memory extension technology.
+
+2) Sure there may be performance advantages in some situations, but
+   what's the space/time overhead of frontswap?
+
+If CONFIG_FRONTSWAP is disabled, every frontswap hook compiles into
+nothingness and the only overhead is a few extra bytes per swapon'ed
+swap device.  If CONFIG_FRONTSWAP is enabled but no frontswap "backend"
+registers, there is one extra global variable compared to zero for
+every swap page read or written.  If CONFIG_FRONTSWAP is enabled
+AND a frontswap backend registers AND the backend fails every "store"
+request (i.e. provides no memory despite claiming it might),
+CPU overhead is still negligible -- and since every frontswap fail
+precedes a swap page write-to-disk, the system is highly likely
+to be I/O bound and using a small fraction of a percent of a CPU
+will be irrelevant anyway.
+
+As for space, if CONFIG_FRONTSWAP is enabled AND a frontswap backend
+registers, one bit is allocated for every swap page for every swap
+device that is swapon'd.  This is added to the EIGHT bits (which
+was sixteen until about 2.6.34) that the kernel already allocates
+for every swap page for every swap device that is swapon'd.  (Hugh
+Dickins has observed that frontswap could probably steal one of
+the existing eight bits, but let's worry about that minor optimization
+later.)  For very large swap disks (which are rare) on a standard
+4K pagesize, this is 1MB per 32GB swap.
+
+When swap pages are stored in transcendent memory instead of written
+out to disk, there is a side effect that this may create more memory
+pressure that can potentially outweigh the other advantages.  A
+backend, such as zcache, must implement policies to carefully (but
+dynamically) manage memory limits to ensure this doesn't happen.
+
+3) OK, how about a quick overview of what this frontswap patch does
+   in terms that a kernel hacker can grok?
+
+Let's assume that a frontswap "backend" has registered during
+kernel initialization; this registration indicates that this
+frontswap backend has access to some "memory" that is not directly
+accessible by the kernel.  Exactly how much memory it provides is
+entirely dynamic and random.
+
+Whenever a swap-device is swapon'd frontswap_init() is called,
+passing the swap device number (aka "type") as a parameter.
+This notifies frontswap to expect attempts to "store" swap pages
+associated with that number.
+
+Whenever the swap subsystem is readying a page to write to a swap
+device (c.f swap_writepage()), frontswap_store is called.  Frontswap
+consults with the frontswap backend and if the backend says it does NOT
+have room, frontswap_store returns -1 and the kernel swaps the page
+to the swap device as normal.  Note that the response from the frontswap
+backend is unpredictable to the kernel; it may choose to never accept a
+page, it could accept every ninth page, or it might accept every
+page.  But if the backend does accept a page, the data from the page
+has already been copied and associated with the type and offset,
+and the backend guarantees the persistence of the data.  In this case,
+frontswap sets a bit in the "frontswap_map" for the swap device
+corresponding to the page offset on the swap device to which it would
+otherwise have written the data.
+
+When the swap subsystem needs to swap-in a page (swap_readpage()),
+it first calls frontswap_load() which checks the frontswap_map to
+see if the page was earlier accepted by the frontswap backend.  If
+it was, the page of data is filled from the frontswap backend and
+the swap-in is complete.  If not, the normal swap-in code is
+executed to obtain the page of data from the real swap device.
+
+So every time the frontswap backend accepts a page, a swap device read
+and (potentially) a swap device write are replaced by a "frontswap backend
+store" and (possibly) a "frontswap backend loads", which are presumably much
+faster.
+
+4) Can't frontswap be configured as a "special" swap device that is
+   just higher priority than any real swap device (e.g. like zswap,
+   or maybe swap-over-nbd/NFS)?
+
+No.  First, the existing swap subsystem doesn't allow for any kind of
+swap hierarchy.  Perhaps it could be rewritten to accomodate a hierarchy,
+but this would require fairly drastic changes.  Even if it were
+rewritten, the existing swap subsystem uses the block I/O layer which
+assumes a swap device is fixed size and any page in it is linearly
+addressable.  Frontswap barely touches the existing swap subsystem,
+and works around the constraints of the block I/O subsystem to provide
+a great deal of flexibility and dynamicity.
+
+For example, the acceptance of any swap page by the frontswap backend is
+entirely unpredictable. This is critical to the definition of frontswap
+backends because it grants completely dynamic discretion to the
+backend.  In zcache, one cannot know a priori how compressible a page is.
+"Poorly" compressible pages can be rejected, and "poorly" can itself be
+defined dynamically depending on current memory constraints.
+
+Further, frontswap is entirely synchronous whereas a real swap
+device is, by definition, asynchronous and uses block I/O.  The
+block I/O layer is not only unnecessary, but may perform "optimizations"
+that are inappropriate for a RAM-oriented device including delaying
+the write of some pages for a significant amount of time.  Synchrony is
+required to ensure the dynamicity of the backend and to avoid thorny race
+conditions that would unnecessarily and greatly complicate frontswap
+and/or the block I/O subsystem.  That said, only the initial "store"
+and "load" operations need be synchronous.  A separate asynchronous thread
+is free to manipulate the pages stored by frontswap.  For example,
+the "remotification" thread in RAMster uses standard asynchronous
+kernel sockets to move compressed frontswap pages to a remote machine.
+Similarly, a KVM guest-side implementation could do in-guest compression
+and use "batched" hypercalls.
+
+In a virtualized environment, the dynamicity allows the hypervisor
+(or host OS) to do "intelligent overcommit".  For example, it can
+choose to accept pages only until host-swapping might be imminent,
+then force guests to do their own swapping.
+
+There is a downside to the transcendent memory specifications for
+frontswap:  Since any "store" might fail, there must always be a real
+slot on a real swap device to swap the page.  Thus frontswap must be
+implemented as a "shadow" to every swapon'd device with the potential
+capability of holding every page that the swap device might have held
+and the possibility that it might hold no pages at all.  This means
+that frontswap cannot contain more pages than the total of swapon'd
+swap devices.  For example, if NO swap device is configured on some
+installation, frontswap is useless.  Swapless portable devices
+can still use frontswap but a backend for such devices must configure
+some kind of "ghost" swap device and ensure that it is never used.
+
+5) Why this weird definition about "duplicate stores"?  If a page
+   has been previously successfully stored, can't it always be
+   successfully overwritten?
+
+Nearly always it can, but no, sometimes it cannot.  Consider an example
+where data is compressed and the original 4K page has been compressed
+to 1K.  Now an attempt is made to overwrite the page with data that
+is non-compressible and so would take the entire 4K.  But the backend
+has no more space.  In this case, the store must be rejected.  Whenever
+frontswap rejects a store that would overwrite, it also must invalidate
+the old data and ensure that it is no longer accessible.  Since the
+swap subsystem then writes the new data to the read swap device,
+this is the correct course of action to ensure coherency.
+
+6) What is frontswap_shrink for?
+
+When the (non-frontswap) swap subsystem swaps out a page to a real
+swap device, that page is only taking up low-value pre-allocated disk
+space.  But if frontswap has placed a page in transcendent memory, that
+page may be taking up valuable real estate.  The frontswap_shrink
+routine allows code outside of the swap subsystem to force pages out
+of the memory managed by frontswap and back into kernel-addressable memory.
+For example, in RAMster, a "suction driver" thread will attempt
+to "repatriate" pages sent to a remote machine back to the local machine;
+this is driven using the frontswap_shrink mechanism when memory pressure
+subsides.
+
+7) Why does the frontswap patch create the new include file swapfile.h?
+
+The frontswap code depends on some swap-subsystem-internal data
+structures that have, over the years, moved back and forth between
+static and global.  This seemed a reasonable compromise:  Define
+them as global but declare them in a new include file that isn't
+included by the large number of source files that include swap.h.
+
+Dan Magenheimer, last updated April 9, 2012
diff --git a/MAINTAINERS b/MAINTAINERS
index 55f0fda..6a52bb4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2930,6 +2930,13 @@
 F:	include/linux/freezer.h
 F:	kernel/freezer.c
 
+FRONTSWAP API
+M:	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
+L:	linux-kernel@vger.kernel.org
+S:	Maintained
+F:	mm/frontswap.c
+F:	include/linux/frontswap.h
+
 FS-CACHE: LOCAL CACHING FOR NETWORK FILESYSTEMS
 M:	David Howells <dhowells@redhat.com>
 L:	linux-cachefs@redhat.com
diff --git a/arch/avr32/kernel/signal.c b/arch/avr32/kernel/signal.c
index c140f9b..d552a85 100644
--- a/arch/avr32/kernel/signal.c
+++ b/arch/avr32/kernel/signal.c
@@ -300,7 +300,7 @@
 	if ((sysreg_read(SR) & MODE_MASK) == MODE_SUPERVISOR)
 		syscall = 1;
 
-	if (ti->flags & _TIF_SIGPENDING))
+	if (ti->flags & _TIF_SIGPENDING)
 		do_signal(regs, syscall);
 
 	if (ti->flags & _TIF_NOTIFY_RESUME) {
diff --git a/arch/xtensa/include/asm/syscall.h b/arch/xtensa/include/asm/syscall.h
index 0b9f2e1..c1dacca 100644
--- a/arch/xtensa/include/asm/syscall.h
+++ b/arch/xtensa/include/asm/syscall.h
@@ -31,5 +31,5 @@
 asmlinkage long sys_ppoll(struct pollfd __user *ufds, unsigned int nfds,
 	struct timespec __user *tsp, const sigset_t __user *sigmask,
 	size_t sigsetsize);
-
-
+asmlinkage long sys_rt_sigsuspend(sigset_t __user *unewset,
+		size_t sigsetsize);
diff --git a/arch/xtensa/kernel/signal.c b/arch/xtensa/kernel/signal.c
index b9f8e58..efe4e85 100644
--- a/arch/xtensa/kernel/signal.c
+++ b/arch/xtensa/kernel/signal.c
@@ -493,7 +493,7 @@
 		if (ret)
 			return;
 
-		signal_delivered(signr, info, ka, regs, 0);
+		signal_delivered(signr, &info, &ka, regs, 0);
 		if (current->ptrace & PT_SINGLESTEP)
 			task_pt_regs(current)->icountlevel = 1;
 
diff --git a/drivers/staging/ramster/zcache-main.c b/drivers/staging/ramster/zcache-main.c
index 4e7ef0e..d46764b 100644
--- a/drivers/staging/ramster/zcache-main.c
+++ b/drivers/staging/ramster/zcache-main.c
@@ -3002,7 +3002,7 @@
 	return oid;
 }
 
-static int zcache_frontswap_put_page(unsigned type, pgoff_t offset,
+static int zcache_frontswap_store(unsigned type, pgoff_t offset,
 				   struct page *page)
 {
 	u64 ind64 = (u64)offset;
@@ -3025,7 +3025,7 @@
 
 /* returns 0 if the page was successfully gotten from frontswap, -1 if
  * was not present (should never happen!) */
-static int zcache_frontswap_get_page(unsigned type, pgoff_t offset,
+static int zcache_frontswap_load(unsigned type, pgoff_t offset,
 				   struct page *page)
 {
 	u64 ind64 = (u64)offset;
@@ -3080,8 +3080,8 @@
 }
 
 static struct frontswap_ops zcache_frontswap_ops = {
-	.put_page = zcache_frontswap_put_page,
-	.get_page = zcache_frontswap_get_page,
+	.store = zcache_frontswap_store,
+	.load = zcache_frontswap_load,
 	.invalidate_page = zcache_frontswap_flush_page,
 	.invalidate_area = zcache_frontswap_flush_area,
 	.init = zcache_frontswap_init
diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index 2734dac..784c796 100644
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -1835,7 +1835,7 @@
  * Swizzling increases objects per swaptype, increasing tmem concurrency
  * for heavy swaploads.  Later, larger nr_cpus -> larger SWIZ_BITS
  * Setting SWIZ_BITS to 27 basically reconstructs the swap entry from
- * frontswap_get_page(), but has side-effects. Hence using 8.
+ * frontswap_load(), but has side-effects. Hence using 8.
  */
 #define SWIZ_BITS		8
 #define SWIZ_MASK		((1 << SWIZ_BITS) - 1)
@@ -1849,7 +1849,7 @@
 	return oid;
 }
 
-static int zcache_frontswap_put_page(unsigned type, pgoff_t offset,
+static int zcache_frontswap_store(unsigned type, pgoff_t offset,
 				   struct page *page)
 {
 	u64 ind64 = (u64)offset;
@@ -1870,7 +1870,7 @@
 
 /* returns 0 if the page was successfully gotten from frontswap, -1 if
  * was not present (should never happen!) */
-static int zcache_frontswap_get_page(unsigned type, pgoff_t offset,
+static int zcache_frontswap_load(unsigned type, pgoff_t offset,
 				   struct page *page)
 {
 	u64 ind64 = (u64)offset;
@@ -1919,8 +1919,8 @@
 }
 
 static struct frontswap_ops zcache_frontswap_ops = {
-	.put_page = zcache_frontswap_put_page,
-	.get_page = zcache_frontswap_get_page,
+	.store = zcache_frontswap_store,
+	.load = zcache_frontswap_load,
 	.invalidate_page = zcache_frontswap_flush_page,
 	.invalidate_area = zcache_frontswap_flush_area,
 	.init = zcache_frontswap_init
diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c
index dcb79521..89f264c 100644
--- a/drivers/xen/tmem.c
+++ b/drivers/xen/tmem.c
@@ -269,7 +269,7 @@
 }
 
 /* returns 0 if the page was successfully put into frontswap, -1 if not */
-static int tmem_frontswap_put_page(unsigned type, pgoff_t offset,
+static int tmem_frontswap_store(unsigned type, pgoff_t offset,
 				   struct page *page)
 {
 	u64 ind64 = (u64)offset;
@@ -295,7 +295,7 @@
  * returns 0 if the page was successfully gotten from frontswap, -1 if
  * was not present (should never happen!)
  */
-static int tmem_frontswap_get_page(unsigned type, pgoff_t offset,
+static int tmem_frontswap_load(unsigned type, pgoff_t offset,
 				   struct page *page)
 {
 	u64 ind64 = (u64)offset;
@@ -362,8 +362,8 @@
 __setup("nofrontswap", no_frontswap);
 
 static struct frontswap_ops __initdata tmem_frontswap_ops = {
-	.put_page = tmem_frontswap_put_page,
-	.get_page = tmem_frontswap_get_page,
+	.store = tmem_frontswap_store,
+	.load = tmem_frontswap_load,
 	.invalidate_page = tmem_frontswap_flush_page,
 	.invalidate_area = tmem_frontswap_flush_area,
 	.init = tmem_frontswap_init
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 20350a9..6df0cbe 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -174,6 +174,7 @@
 	void (*add_credits)(struct TCP_Server_Info *, const unsigned int);
 	void (*set_credits)(struct TCP_Server_Info *, const int);
 	int * (*get_credits_field)(struct TCP_Server_Info *);
+	__u64 (*get_next_mid)(struct TCP_Server_Info *);
 	/* data offset from read response message */
 	unsigned int (*read_data_offset)(char *);
 	/* data length from read response message */
@@ -399,6 +400,12 @@
 	server->ops->set_credits(server, val);
 }
 
+static inline __u64
+get_next_mid(struct TCP_Server_Info *server)
+{
+	return server->ops->get_next_mid(server);
+}
+
 /*
  * Macros to allow the TCP_Server_Info->net field and related code to drop out
  * when CONFIG_NET_NS isn't set.
diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
index 5ec21ec..0a6cbfe 100644
--- a/fs/cifs/cifsproto.h
+++ b/fs/cifs/cifsproto.h
@@ -114,7 +114,6 @@
 				void **request_buf);
 extern int CIFS_SessSetup(unsigned int xid, struct cifs_ses *ses,
 			     const struct nls_table *nls_cp);
-extern __u64 GetNextMid(struct TCP_Server_Info *server);
 extern struct timespec cifs_NTtimeToUnix(__le64 utc_nanoseconds_since_1601);
 extern u64 cifs_UnixTimeToNT(struct timespec);
 extern struct timespec cnvrtDosUnixTm(__le16 le_date, __le16 le_time,
diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index b5ad716..5b40073 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -268,7 +268,7 @@
 		return rc;
 
 	buffer = (struct smb_hdr *)*request_buf;
-	buffer->Mid = GetNextMid(ses->server);
+	buffer->Mid = get_next_mid(ses->server);
 	if (ses->capabilities & CAP_UNICODE)
 		buffer->Flags2 |= SMBFLG2_UNICODE;
 	if (ses->capabilities & CAP_STATUS32)
@@ -402,7 +402,7 @@
 
 	cFYI(1, "secFlags 0x%x", secFlags);
 
-	pSMB->hdr.Mid = GetNextMid(server);
+	pSMB->hdr.Mid = get_next_mid(server);
 	pSMB->hdr.Flags2 |= (SMBFLG2_UNICODE | SMBFLG2_ERR_STATUS);
 
 	if ((secFlags & CIFSSEC_MUST_KRB5) == CIFSSEC_MUST_KRB5)
@@ -782,7 +782,7 @@
 		return rc;
 	}
 
-	pSMB->hdr.Mid = GetNextMid(ses->server);
+	pSMB->hdr.Mid = get_next_mid(ses->server);
 
 	if (ses->server->sec_mode &
 		   (SECMODE_SIGN_REQUIRED | SECMODE_SIGN_ENABLED))
@@ -4762,7 +4762,7 @@
 
 	/* server pointer checked in called function,
 	but should never be null here anyway */
-	pSMB->hdr.Mid = GetNextMid(ses->server);
+	pSMB->hdr.Mid = get_next_mid(ses->server);
 	pSMB->hdr.Tid = ses->ipc_tid;
 	pSMB->hdr.Uid = ses->Suid;
 	if (ses->capabilities & CAP_STATUS32)
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index ccafded..78db68a 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -1058,13 +1058,15 @@
 		if (mid_entry != NULL) {
 			if (!mid_entry->multiRsp || mid_entry->multiEnd)
 				mid_entry->callback(mid_entry);
-		} else if (!server->ops->is_oplock_break(buf, server)) {
+		} else if (!server->ops->is_oplock_break ||
+			   !server->ops->is_oplock_break(buf, server)) {
 			cERROR(1, "No task to wake, unknown frame received! "
 				   "NumMids %d", atomic_read(&midCount));
 			cifs_dump_mem("Received Data is: ", buf,
 				      HEADER_SIZE(server));
 #ifdef CONFIG_CIFS_DEBUG2
-			server->ops->dump_detail(buf);
+			if (server->ops->dump_detail)
+				server->ops->dump_detail(buf);
 			cifs_dump_mids(server);
 #endif /* CIFS_DEBUG2 */
 
@@ -3938,7 +3940,7 @@
 	header_assemble(smb_buffer, SMB_COM_TREE_CONNECT_ANDX,
 			NULL /*no tid */ , 4 /*wct */ );
 
-	smb_buffer->Mid = GetNextMid(ses->server);
+	smb_buffer->Mid = get_next_mid(ses->server);
 	smb_buffer->Uid = ses->Suid;
 	pSMB = (TCONX_REQ *) smb_buffer;
 	pSMBr = (TCONX_RSP *) smb_buffer_response;
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 253170d..513adbc 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -876,7 +876,7 @@
 	struct cifsLockInfo *li, *tmp;
 	struct cifs_tcon *tcon;
 	struct cifsInodeInfo *cinode = CIFS_I(cfile->dentry->d_inode);
-	unsigned int num, max_num;
+	unsigned int num, max_num, max_buf;
 	LOCKING_ANDX_RANGE *buf, *cur;
 	int types[] = {LOCKING_ANDX_LARGE_FILES,
 		       LOCKING_ANDX_SHARED_LOCK | LOCKING_ANDX_LARGE_FILES};
@@ -892,8 +892,19 @@
 		return rc;
 	}
 
-	max_num = (tcon->ses->server->maxBuf - sizeof(struct smb_hdr)) /
-		  sizeof(LOCKING_ANDX_RANGE);
+	/*
+	 * Accessing maxBuf is racy with cifs_reconnect - need to store value
+	 * and check it for zero before using.
+	 */
+	max_buf = tcon->ses->server->maxBuf;
+	if (!max_buf) {
+		mutex_unlock(&cinode->lock_mutex);
+		FreeXid(xid);
+		return -EINVAL;
+	}
+
+	max_num = (max_buf - sizeof(struct smb_hdr)) /
+						sizeof(LOCKING_ANDX_RANGE);
 	buf = kzalloc(max_num * sizeof(LOCKING_ANDX_RANGE), GFP_KERNEL);
 	if (!buf) {
 		mutex_unlock(&cinode->lock_mutex);
@@ -1218,7 +1229,7 @@
 	int types[] = {LOCKING_ANDX_LARGE_FILES,
 		       LOCKING_ANDX_SHARED_LOCK | LOCKING_ANDX_LARGE_FILES};
 	unsigned int i;
-	unsigned int max_num, num;
+	unsigned int max_num, num, max_buf;
 	LOCKING_ANDX_RANGE *buf, *cur;
 	struct cifs_tcon *tcon = tlink_tcon(cfile->tlink);
 	struct cifsInodeInfo *cinode = CIFS_I(cfile->dentry->d_inode);
@@ -1228,8 +1239,16 @@
 
 	INIT_LIST_HEAD(&tmp_llist);
 
-	max_num = (tcon->ses->server->maxBuf - sizeof(struct smb_hdr)) /
-		  sizeof(LOCKING_ANDX_RANGE);
+	/*
+	 * Accessing maxBuf is racy with cifs_reconnect - need to store value
+	 * and check it for zero before using.
+	 */
+	max_buf = tcon->ses->server->maxBuf;
+	if (!max_buf)
+		return -EINVAL;
+
+	max_num = (max_buf - sizeof(struct smb_hdr)) /
+						sizeof(LOCKING_ANDX_RANGE);
 	buf = kzalloc(max_num * sizeof(LOCKING_ANDX_RANGE), GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
@@ -1247,46 +1266,7 @@
 				continue;
 			if (types[i] != li->type)
 				continue;
-			if (!cinode->can_cache_brlcks) {
-				cur->Pid = cpu_to_le16(li->pid);
-				cur->LengthLow = cpu_to_le32((u32)li->length);
-				cur->LengthHigh =
-					cpu_to_le32((u32)(li->length>>32));
-				cur->OffsetLow = cpu_to_le32((u32)li->offset);
-				cur->OffsetHigh =
-					cpu_to_le32((u32)(li->offset>>32));
-				/*
-				 * We need to save a lock here to let us add
-				 * it again to the file's list if the unlock
-				 * range request fails on the server.
-				 */
-				list_move(&li->llist, &tmp_llist);
-				if (++num == max_num) {
-					stored_rc = cifs_lockv(xid, tcon,
-							       cfile->netfid,
-							       li->type, num,
-							       0, buf);
-					if (stored_rc) {
-						/*
-						 * We failed on the unlock range
-						 * request - add all locks from
-						 * the tmp list to the head of
-						 * the file's list.
-						 */
-						cifs_move_llist(&tmp_llist,
-								&cfile->llist);
-						rc = stored_rc;
-					} else
-						/*
-						 * The unlock range request
-						 * succeed - free the tmp list.
-						 */
-						cifs_free_llist(&tmp_llist);
-					cur = buf;
-					num = 0;
-				} else
-					cur++;
-			} else {
+			if (cinode->can_cache_brlcks) {
 				/*
 				 * We can cache brlock requests - simply remove
 				 * a lock from the file's list.
@@ -1294,7 +1274,41 @@
 				list_del(&li->llist);
 				cifs_del_lock_waiters(li);
 				kfree(li);
+				continue;
 			}
+			cur->Pid = cpu_to_le16(li->pid);
+			cur->LengthLow = cpu_to_le32((u32)li->length);
+			cur->LengthHigh = cpu_to_le32((u32)(li->length>>32));
+			cur->OffsetLow = cpu_to_le32((u32)li->offset);
+			cur->OffsetHigh = cpu_to_le32((u32)(li->offset>>32));
+			/*
+			 * We need to save a lock here to let us add it again to
+			 * the file's list if the unlock range request fails on
+			 * the server.
+			 */
+			list_move(&li->llist, &tmp_llist);
+			if (++num == max_num) {
+				stored_rc = cifs_lockv(xid, tcon, cfile->netfid,
+						       li->type, num, 0, buf);
+				if (stored_rc) {
+					/*
+					 * We failed on the unlock range
+					 * request - add all locks from the tmp
+					 * list to the head of the file's list.
+					 */
+					cifs_move_llist(&tmp_llist,
+							&cfile->llist);
+					rc = stored_rc;
+				} else
+					/*
+					 * The unlock range request succeed -
+					 * free the tmp list.
+					 */
+					cifs_free_llist(&tmp_llist);
+				cur = buf;
+				num = 0;
+			} else
+				cur++;
 		}
 		if (num) {
 			stored_rc = cifs_lockv(xid, tcon, cfile->netfid,
diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index e2552d2..557506a 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -212,93 +212,6 @@
 	return;
 }
 
-/*
- * Find a free multiplex id (SMB mid). Otherwise there could be
- * mid collisions which might cause problems, demultiplexing the
- * wrong response to this request. Multiplex ids could collide if
- * one of a series requests takes much longer than the others, or
- * if a very large number of long lived requests (byte range
- * locks or FindNotify requests) are pending. No more than
- * 64K-1 requests can be outstanding at one time. If no
- * mids are available, return zero. A future optimization
- * could make the combination of mids and uid the key we use
- * to demultiplex on (rather than mid alone).
- * In addition to the above check, the cifs demultiplex
- * code already used the command code as a secondary
- * check of the frame and if signing is negotiated the
- * response would be discarded if the mid were the same
- * but the signature was wrong. Since the mid is not put in the
- * pending queue until later (when it is about to be dispatched)
- * we do have to limit the number of outstanding requests
- * to somewhat less than 64K-1 although it is hard to imagine
- * so many threads being in the vfs at one time.
- */
-__u64 GetNextMid(struct TCP_Server_Info *server)
-{
-	__u64 mid = 0;
-	__u16 last_mid, cur_mid;
-	bool collision;
-
-	spin_lock(&GlobalMid_Lock);
-
-	/* mid is 16 bit only for CIFS/SMB */
-	cur_mid = (__u16)((server->CurrentMid) & 0xffff);
-	/* we do not want to loop forever */
-	last_mid = cur_mid;
-	cur_mid++;
-
-	/*
-	 * This nested loop looks more expensive than it is.
-	 * In practice the list of pending requests is short,
-	 * fewer than 50, and the mids are likely to be unique
-	 * on the first pass through the loop unless some request
-	 * takes longer than the 64 thousand requests before it
-	 * (and it would also have to have been a request that
-	 * did not time out).
-	 */
-	while (cur_mid != last_mid) {
-		struct mid_q_entry *mid_entry;
-		unsigned int num_mids;
-
-		collision = false;
-		if (cur_mid == 0)
-			cur_mid++;
-
-		num_mids = 0;
-		list_for_each_entry(mid_entry, &server->pending_mid_q, qhead) {
-			++num_mids;
-			if (mid_entry->mid == cur_mid &&
-			    mid_entry->mid_state == MID_REQUEST_SUBMITTED) {
-				/* This mid is in use, try a different one */
-				collision = true;
-				break;
-			}
-		}
-
-		/*
-		 * if we have more than 32k mids in the list, then something
-		 * is very wrong. Possibly a local user is trying to DoS the
-		 * box by issuing long-running calls and SIGKILL'ing them. If
-		 * we get to 2^16 mids then we're in big trouble as this
-		 * function could loop forever.
-		 *
-		 * Go ahead and assign out the mid in this situation, but force
-		 * an eventual reconnect to clean out the pending_mid_q.
-		 */
-		if (num_mids > 32768)
-			server->tcpStatus = CifsNeedReconnect;
-
-		if (!collision) {
-			mid = (__u64)cur_mid;
-			server->CurrentMid = mid;
-			break;
-		}
-		cur_mid++;
-	}
-	spin_unlock(&GlobalMid_Lock);
-	return mid;
-}
-
 /* NB: MID can not be set if treeCon not passed in, in that
    case it is responsbility of caller to set the mid */
 void
@@ -334,7 +247,7 @@
 
 			/* Uid is not converted */
 			buffer->Uid = treeCon->ses->Suid;
-			buffer->Mid = GetNextMid(treeCon->ses->server);
+			buffer->Mid = get_next_mid(treeCon->ses->server);
 		}
 		if (treeCon->Flags & SMB_SHARE_IS_IN_DFS)
 			buffer->Flags2 |= SMBFLG2_DFS;
diff --git a/fs/cifs/smb1ops.c b/fs/cifs/smb1ops.c
index d9d615f..6dec38f 100644
--- a/fs/cifs/smb1ops.c
+++ b/fs/cifs/smb1ops.c
@@ -125,6 +125,94 @@
 	return &server->credits;
 }
 
+/*
+ * Find a free multiplex id (SMB mid). Otherwise there could be
+ * mid collisions which might cause problems, demultiplexing the
+ * wrong response to this request. Multiplex ids could collide if
+ * one of a series requests takes much longer than the others, or
+ * if a very large number of long lived requests (byte range
+ * locks or FindNotify requests) are pending. No more than
+ * 64K-1 requests can be outstanding at one time. If no
+ * mids are available, return zero. A future optimization
+ * could make the combination of mids and uid the key we use
+ * to demultiplex on (rather than mid alone).
+ * In addition to the above check, the cifs demultiplex
+ * code already used the command code as a secondary
+ * check of the frame and if signing is negotiated the
+ * response would be discarded if the mid were the same
+ * but the signature was wrong. Since the mid is not put in the
+ * pending queue until later (when it is about to be dispatched)
+ * we do have to limit the number of outstanding requests
+ * to somewhat less than 64K-1 although it is hard to imagine
+ * so many threads being in the vfs at one time.
+ */
+static __u64
+cifs_get_next_mid(struct TCP_Server_Info *server)
+{
+	__u64 mid = 0;
+	__u16 last_mid, cur_mid;
+	bool collision;
+
+	spin_lock(&GlobalMid_Lock);
+
+	/* mid is 16 bit only for CIFS/SMB */
+	cur_mid = (__u16)((server->CurrentMid) & 0xffff);
+	/* we do not want to loop forever */
+	last_mid = cur_mid;
+	cur_mid++;
+
+	/*
+	 * This nested loop looks more expensive than it is.
+	 * In practice the list of pending requests is short,
+	 * fewer than 50, and the mids are likely to be unique
+	 * on the first pass through the loop unless some request
+	 * takes longer than the 64 thousand requests before it
+	 * (and it would also have to have been a request that
+	 * did not time out).
+	 */
+	while (cur_mid != last_mid) {
+		struct mid_q_entry *mid_entry;
+		unsigned int num_mids;
+
+		collision = false;
+		if (cur_mid == 0)
+			cur_mid++;
+
+		num_mids = 0;
+		list_for_each_entry(mid_entry, &server->pending_mid_q, qhead) {
+			++num_mids;
+			if (mid_entry->mid == cur_mid &&
+			    mid_entry->mid_state == MID_REQUEST_SUBMITTED) {
+				/* This mid is in use, try a different one */
+				collision = true;
+				break;
+			}
+		}
+
+		/*
+		 * if we have more than 32k mids in the list, then something
+		 * is very wrong. Possibly a local user is trying to DoS the
+		 * box by issuing long-running calls and SIGKILL'ing them. If
+		 * we get to 2^16 mids then we're in big trouble as this
+		 * function could loop forever.
+		 *
+		 * Go ahead and assign out the mid in this situation, but force
+		 * an eventual reconnect to clean out the pending_mid_q.
+		 */
+		if (num_mids > 32768)
+			server->tcpStatus = CifsNeedReconnect;
+
+		if (!collision) {
+			mid = (__u64)cur_mid;
+			server->CurrentMid = mid;
+			break;
+		}
+		cur_mid++;
+	}
+	spin_unlock(&GlobalMid_Lock);
+	return mid;
+}
+
 struct smb_version_operations smb1_operations = {
 	.send_cancel = send_nt_cancel,
 	.compare_fids = cifs_compare_fids,
@@ -133,6 +221,7 @@
 	.add_credits = cifs_add_credits,
 	.set_credits = cifs_set_credits,
 	.get_credits_field = cifs_get_credits_field,
+	.get_next_mid = cifs_get_next_mid,
 	.read_data_offset = cifs_read_data_offset,
 	.read_data_length = cifs_read_data_length,
 	.map_error = map_smb_to_linux_error,
diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index 1b36ffe..3097ee5 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -779,7 +779,7 @@
 
 	pSMB->LockType = LOCKING_ANDX_CANCEL_LOCK|LOCKING_ANDX_LARGE_FILES;
 	pSMB->Timeout = 0;
-	pSMB->hdr.Mid = GetNextMid(ses->server);
+	pSMB->hdr.Mid = get_next_mid(ses->server);
 
 	return SendReceive(xid, ses, in_buf, out_buf,
 			&bytes_returned, 0);
diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
new file mode 100644
index 0000000..0e4e2ee
--- /dev/null
+++ b/include/linux/frontswap.h
@@ -0,0 +1,127 @@
+#ifndef _LINUX_FRONTSWAP_H
+#define _LINUX_FRONTSWAP_H
+
+#include <linux/swap.h>
+#include <linux/mm.h>
+#include <linux/bitops.h>
+
+struct frontswap_ops {
+	void (*init)(unsigned);
+	int (*store)(unsigned, pgoff_t, struct page *);
+	int (*load)(unsigned, pgoff_t, struct page *);
+	void (*invalidate_page)(unsigned, pgoff_t);
+	void (*invalidate_area)(unsigned);
+};
+
+extern bool frontswap_enabled;
+extern struct frontswap_ops
+	frontswap_register_ops(struct frontswap_ops *ops);
+extern void frontswap_shrink(unsigned long);
+extern unsigned long frontswap_curr_pages(void);
+extern void frontswap_writethrough(bool);
+
+extern void __frontswap_init(unsigned type);
+extern int __frontswap_store(struct page *page);
+extern int __frontswap_load(struct page *page);
+extern void __frontswap_invalidate_page(unsigned, pgoff_t);
+extern void __frontswap_invalidate_area(unsigned);
+
+#ifdef CONFIG_FRONTSWAP
+
+static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
+{
+	bool ret = false;
+
+	if (frontswap_enabled && sis->frontswap_map)
+		ret = test_bit(offset, sis->frontswap_map);
+	return ret;
+}
+
+static inline void frontswap_set(struct swap_info_struct *sis, pgoff_t offset)
+{
+	if (frontswap_enabled && sis->frontswap_map)
+		set_bit(offset, sis->frontswap_map);
+}
+
+static inline void frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
+{
+	if (frontswap_enabled && sis->frontswap_map)
+		clear_bit(offset, sis->frontswap_map);
+}
+
+static inline void frontswap_map_set(struct swap_info_struct *p,
+				     unsigned long *map)
+{
+	p->frontswap_map = map;
+}
+
+static inline unsigned long *frontswap_map_get(struct swap_info_struct *p)
+{
+	return p->frontswap_map;
+}
+#else
+/* all inline routines become no-ops and all externs are ignored */
+
+#define frontswap_enabled (0)
+
+static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
+{
+	return false;
+}
+
+static inline void frontswap_set(struct swap_info_struct *sis, pgoff_t offset)
+{
+}
+
+static inline void frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
+{
+}
+
+static inline void frontswap_map_set(struct swap_info_struct *p,
+				     unsigned long *map)
+{
+}
+
+static inline unsigned long *frontswap_map_get(struct swap_info_struct *p)
+{
+	return NULL;
+}
+#endif
+
+static inline int frontswap_store(struct page *page)
+{
+	int ret = -1;
+
+	if (frontswap_enabled)
+		ret = __frontswap_store(page);
+	return ret;
+}
+
+static inline int frontswap_load(struct page *page)
+{
+	int ret = -1;
+
+	if (frontswap_enabled)
+		ret = __frontswap_load(page);
+	return ret;
+}
+
+static inline void frontswap_invalidate_page(unsigned type, pgoff_t offset)
+{
+	if (frontswap_enabled)
+		__frontswap_invalidate_page(type, offset);
+}
+
+static inline void frontswap_invalidate_area(unsigned type)
+{
+	if (frontswap_enabled)
+		__frontswap_invalidate_area(type);
+}
+
+static inline void frontswap_init(unsigned type)
+{
+	if (frontswap_enabled)
+		__frontswap_init(type);
+}
+
+#endif /* _LINUX_FRONTSWAP_H */
diff --git a/include/linux/swap.h b/include/linux/swap.h
index b666193..c84ec68 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -197,6 +197,10 @@
 	struct block_device *bdev;	/* swap device or bdev of swap file */
 	struct file *swap_file;		/* seldom referenced */
 	unsigned int old_block_size;	/* seldom referenced */
+#ifdef CONFIG_FRONTSWAP
+	unsigned long *frontswap_map;	/* frontswap in-use, one bit per page */
+	atomic_t frontswap_pages;	/* frontswap pages in-use counter */
+#endif
 };
 
 struct swap_list_t {
diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h
new file mode 100644
index 0000000..e282624
--- /dev/null
+++ b/include/linux/swapfile.h
@@ -0,0 +1,13 @@
+#ifndef _LINUX_SWAPFILE_H
+#define _LINUX_SWAPFILE_H
+
+/*
+ * these were static in swapfile.c but frontswap.c needs them and we don't
+ * want to expose them to the dozens of source files that include swap.h
+ */
+extern spinlock_t swap_lock;
+extern struct swap_list_t swap_list;
+extern struct swap_info_struct *swap_info[];
+extern int try_to_unuse(unsigned int, bool, unsigned long);
+
+#endif /* _LINUX_SWAPFILE_H */
diff --git a/mm/Kconfig b/mm/Kconfig
index b217637..82fed4e 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -389,3 +389,20 @@
 	  in a negligible performance hit.
 
 	  If unsure, say Y to enable cleancache
+
+config FRONTSWAP
+	bool "Enable frontswap to cache swap pages if tmem is present"
+	depends on SWAP
+	default n
+	help
+	  Frontswap is so named because it can be thought of as the opposite
+	  of a "backing" store for a swap device.  The data is stored into
+	  "transcendent memory", memory that is not directly accessible or
+	  addressable by the kernel and is of unknown and possibly
+	  time-varying size.  When space in transcendent memory is available,
+	  a significant swap I/O reduction may be achieved.  When none is
+	  available, all frontswap calls are reduced to a single pointer-
+	  compare-against-NULL resulting in a negligible performance hit
+	  and swap data is stored as normal on the matching swap device.
+
+	  If unsure, say Y to enable frontswap.
diff --git a/mm/Makefile b/mm/Makefile
index a156285..2e2fbbe 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -29,6 +29,7 @@
 
 obj-$(CONFIG_BOUNCE)	+= bounce.o
 obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o
+obj-$(CONFIG_FRONTSWAP)	+= frontswap.o
 obj-$(CONFIG_HAS_DMA)	+= dmapool.o
 obj-$(CONFIG_HUGETLBFS)	+= hugetlb.o
 obj-$(CONFIG_NUMA) 	+= mempolicy.o
diff --git a/mm/frontswap.c b/mm/frontswap.c
new file mode 100644
index 0000000..e250255
--- /dev/null
+++ b/mm/frontswap.c
@@ -0,0 +1,314 @@
+/*
+ * Frontswap frontend
+ *
+ * This code provides the generic "frontend" layer to call a matching
+ * "backend" driver implementation of frontswap.  See
+ * Documentation/vm/frontswap.txt for more information.
+ *
+ * Copyright (C) 2009-2012 Oracle Corp.  All rights reserved.
+ * Author: Dan Magenheimer
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ */
+
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/proc_fs.h>
+#include <linux/security.h>
+#include <linux/capability.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/debugfs.h>
+#include <linux/frontswap.h>
+#include <linux/swapfile.h>
+
+/*
+ * frontswap_ops is set by frontswap_register_ops to contain the pointers
+ * to the frontswap "backend" implementation functions.
+ */
+static struct frontswap_ops frontswap_ops __read_mostly;
+
+/*
+ * This global enablement flag reduces overhead on systems where frontswap_ops
+ * has not been registered, so is preferred to the slower alternative: a
+ * function call that checks a non-global.
+ */
+bool frontswap_enabled __read_mostly;
+EXPORT_SYMBOL(frontswap_enabled);
+
+/*
+ * If enabled, frontswap_store will return failure even on success.  As
+ * a result, the swap subsystem will always write the page to swap, in
+ * effect converting frontswap into a writethrough cache.  In this mode,
+ * there is no direct reduction in swap writes, but a frontswap backend
+ * can unilaterally "reclaim" any pages in use with no data loss, thus
+ * providing increases control over maximum memory usage due to frontswap.
+ */
+static bool frontswap_writethrough_enabled __read_mostly;
+
+#ifdef CONFIG_DEBUG_FS
+/*
+ * Counters available via /sys/kernel/debug/frontswap (if debugfs is
+ * properly configured).  These are for information only so are not protected
+ * against increment races.
+ */
+static u64 frontswap_loads;
+static u64 frontswap_succ_stores;
+static u64 frontswap_failed_stores;
+static u64 frontswap_invalidates;
+
+static inline void inc_frontswap_loads(void) {
+	frontswap_loads++;
+}
+static inline void inc_frontswap_succ_stores(void) {
+	frontswap_succ_stores++;
+}
+static inline void inc_frontswap_failed_stores(void) {
+	frontswap_failed_stores++;
+}
+static inline void inc_frontswap_invalidates(void) {
+	frontswap_invalidates++;
+}
+#else
+static inline void inc_frontswap_loads(void) { }
+static inline void inc_frontswap_succ_stores(void) { }
+static inline void inc_frontswap_failed_stores(void) { }
+static inline void inc_frontswap_invalidates(void) { }
+#endif
+/*
+ * Register operations for frontswap, returning previous thus allowing
+ * detection of multiple backends and possible nesting.
+ */
+struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
+{
+	struct frontswap_ops old = frontswap_ops;
+
+	frontswap_ops = *ops;
+	frontswap_enabled = true;
+	return old;
+}
+EXPORT_SYMBOL(frontswap_register_ops);
+
+/*
+ * Enable/disable frontswap writethrough (see above).
+ */
+void frontswap_writethrough(bool enable)
+{
+	frontswap_writethrough_enabled = enable;
+}
+EXPORT_SYMBOL(frontswap_writethrough);
+
+/*
+ * Called when a swap device is swapon'd.
+ */
+void __frontswap_init(unsigned type)
+{
+	struct swap_info_struct *sis = swap_info[type];
+
+	BUG_ON(sis == NULL);
+	if (sis->frontswap_map == NULL)
+		return;
+	if (frontswap_enabled)
+		(*frontswap_ops.init)(type);
+}
+EXPORT_SYMBOL(__frontswap_init);
+
+/*
+ * "Store" data from a page to frontswap and associate it with the page's
+ * swaptype and offset.  Page must be locked and in the swap cache.
+ * If frontswap already contains a page with matching swaptype and
+ * offset, the frontswap implmentation may either overwrite the data and
+ * return success or invalidate the page from frontswap and return failure.
+ */
+int __frontswap_store(struct page *page)
+{
+	int ret = -1, dup = 0;
+	swp_entry_t entry = { .val = page_private(page), };
+	int type = swp_type(entry);
+	struct swap_info_struct *sis = swap_info[type];
+	pgoff_t offset = swp_offset(entry);
+
+	BUG_ON(!PageLocked(page));
+	BUG_ON(sis == NULL);
+	if (frontswap_test(sis, offset))
+		dup = 1;
+	ret = (*frontswap_ops.store)(type, offset, page);
+	if (ret == 0) {
+		frontswap_set(sis, offset);
+		inc_frontswap_succ_stores();
+		if (!dup)
+			atomic_inc(&sis->frontswap_pages);
+	} else if (dup) {
+		/*
+		  failed dup always results in automatic invalidate of
+		  the (older) page from frontswap
+		 */
+		frontswap_clear(sis, offset);
+		atomic_dec(&sis->frontswap_pages);
+		inc_frontswap_failed_stores();
+	} else
+		inc_frontswap_failed_stores();
+	if (frontswap_writethrough_enabled)
+		/* report failure so swap also writes to swap device */
+		ret = -1;
+	return ret;
+}
+EXPORT_SYMBOL(__frontswap_store);
+
+/*
+ * "Get" data from frontswap associated with swaptype and offset that were
+ * specified when the data was put to frontswap and use it to fill the
+ * specified page with data. Page must be locked and in the swap cache.
+ */
+int __frontswap_load(struct page *page)
+{
+	int ret = -1;
+	swp_entry_t entry = { .val = page_private(page), };
+	int type = swp_type(entry);
+	struct swap_info_struct *sis = swap_info[type];
+	pgoff_t offset = swp_offset(entry);
+
+	BUG_ON(!PageLocked(page));
+	BUG_ON(sis == NULL);
+	if (frontswap_test(sis, offset))
+		ret = (*frontswap_ops.load)(type, offset, page);
+	if (ret == 0)
+		inc_frontswap_loads();
+	return ret;
+}
+EXPORT_SYMBOL(__frontswap_load);
+
+/*
+ * Invalidate any data from frontswap associated with the specified swaptype
+ * and offset so that a subsequent "get" will fail.
+ */
+void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
+{
+	struct swap_info_struct *sis = swap_info[type];
+
+	BUG_ON(sis == NULL);
+	if (frontswap_test(sis, offset)) {
+		(*frontswap_ops.invalidate_page)(type, offset);
+		atomic_dec(&sis->frontswap_pages);
+		frontswap_clear(sis, offset);
+		inc_frontswap_invalidates();
+	}
+}
+EXPORT_SYMBOL(__frontswap_invalidate_page);
+
+/*
+ * Invalidate all data from frontswap associated with all offsets for the
+ * specified swaptype.
+ */
+void __frontswap_invalidate_area(unsigned type)
+{
+	struct swap_info_struct *sis = swap_info[type];
+
+	BUG_ON(sis == NULL);
+	if (sis->frontswap_map == NULL)
+		return;
+	(*frontswap_ops.invalidate_area)(type);
+	atomic_set(&sis->frontswap_pages, 0);
+	memset(sis->frontswap_map, 0, sis->max / sizeof(long));
+}
+EXPORT_SYMBOL(__frontswap_invalidate_area);
+
+/*
+ * Frontswap, like a true swap device, may unnecessarily retain pages
+ * under certain circumstances; "shrink" frontswap is essentially a
+ * "partial swapoff" and works by calling try_to_unuse to attempt to
+ * unuse enough frontswap pages to attempt to -- subject to memory
+ * constraints -- reduce the number of pages in frontswap to the
+ * number given in the parameter target_pages.
+ */
+void frontswap_shrink(unsigned long target_pages)
+{
+	struct swap_info_struct *si = NULL;
+	int si_frontswap_pages;
+	unsigned long total_pages = 0, total_pages_to_unuse;
+	unsigned long pages = 0, pages_to_unuse = 0;
+	int type;
+	bool locked = false;
+
+	/*
+	 * we don't want to hold swap_lock while doing a very
+	 * lengthy try_to_unuse, but swap_list may change
+	 * so restart scan from swap_list.head each time
+	 */
+	spin_lock(&swap_lock);
+	locked = true;
+	total_pages = 0;
+	for (type = swap_list.head; type >= 0; type = si->next) {
+		si = swap_info[type];
+		total_pages += atomic_read(&si->frontswap_pages);
+	}
+	if (total_pages <= target_pages)
+		goto out;
+	total_pages_to_unuse = total_pages - target_pages;
+	for (type = swap_list.head; type >= 0; type = si->next) {
+		si = swap_info[type];
+		si_frontswap_pages = atomic_read(&si->frontswap_pages);
+		if (total_pages_to_unuse < si_frontswap_pages)
+			pages = pages_to_unuse = total_pages_to_unuse;
+		else {
+			pages = si_frontswap_pages;
+			pages_to_unuse = 0; /* unuse all */
+		}
+		/* ensure there is enough RAM to fetch pages from frontswap */
+		if (security_vm_enough_memory_mm(current->mm, pages))
+			continue;
+		vm_unacct_memory(pages);
+		break;
+	}
+	if (type < 0)
+		goto out;
+	locked = false;
+	spin_unlock(&swap_lock);
+	try_to_unuse(type, true, pages_to_unuse);
+out:
+	if (locked)
+		spin_unlock(&swap_lock);
+	return;
+}
+EXPORT_SYMBOL(frontswap_shrink);
+
+/*
+ * Count and return the number of frontswap pages across all
+ * swap devices.  This is exported so that backend drivers can
+ * determine current usage without reading debugfs.
+ */
+unsigned long frontswap_curr_pages(void)
+{
+	int type;
+	unsigned long totalpages = 0;
+	struct swap_info_struct *si = NULL;
+
+	spin_lock(&swap_lock);
+	for (type = swap_list.head; type >= 0; type = si->next) {
+		si = swap_info[type];
+		totalpages += atomic_read(&si->frontswap_pages);
+	}
+	spin_unlock(&swap_lock);
+	return totalpages;
+}
+EXPORT_SYMBOL(frontswap_curr_pages);
+
+static int __init init_frontswap(void)
+{
+#ifdef CONFIG_DEBUG_FS
+	struct dentry *root = debugfs_create_dir("frontswap", NULL);
+	if (root == NULL)
+		return -ENXIO;
+	debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
+	debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
+	debugfs_create_u64("failed_stores", S_IRUGO, root,
+				&frontswap_failed_stores);
+	debugfs_create_u64("invalidates", S_IRUGO,
+				root, &frontswap_invalidates);
+#endif
+	return 0;
+}
+
+module_init(init_frontswap);
diff --git a/mm/page_io.c b/mm/page_io.c
index dc76b4d..34f0292 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -18,6 +18,7 @@
 #include <linux/bio.h>
 #include <linux/swapops.h>
 #include <linux/writeback.h>
+#include <linux/frontswap.h>
 #include <asm/pgtable.h>
 
 static struct bio *get_swap_bio(gfp_t gfp_flags,
@@ -98,6 +99,12 @@
 		unlock_page(page);
 		goto out;
 	}
+	if (frontswap_store(page) == 0) {
+		set_page_writeback(page);
+		unlock_page(page);
+		end_page_writeback(page);
+		goto out;
+	}
 	bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
 	if (bio == NULL) {
 		set_page_dirty(page);
@@ -122,6 +129,11 @@
 
 	VM_BUG_ON(!PageLocked(page));
 	VM_BUG_ON(PageUptodate(page));
+	if (frontswap_load(page) == 0) {
+		SetPageUptodate(page);
+		unlock_page(page);
+		goto out;
+	}
 	bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
 	if (bio == NULL) {
 		unlock_page(page);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 457b10b..de5bc51 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -31,6 +31,8 @@
 #include <linux/memcontrol.h>
 #include <linux/poll.h>
 #include <linux/oom.h>
+#include <linux/frontswap.h>
+#include <linux/swapfile.h>
 
 #include <asm/pgtable.h>
 #include <asm/tlbflush.h>
@@ -42,7 +44,7 @@
 static void free_swap_count_continuations(struct swap_info_struct *);
 static sector_t map_swap_entry(swp_entry_t, struct block_device**);
 
-static DEFINE_SPINLOCK(swap_lock);
+DEFINE_SPINLOCK(swap_lock);
 static unsigned int nr_swapfiles;
 long nr_swap_pages;
 long total_swap_pages;
@@ -53,9 +55,9 @@
 static const char Bad_offset[] = "Bad swap offset entry ";
 static const char Unused_offset[] = "Unused swap offset entry ";
 
-static struct swap_list_t swap_list = {-1, -1};
+struct swap_list_t swap_list = {-1, -1};
 
-static struct swap_info_struct *swap_info[MAX_SWAPFILES];
+struct swap_info_struct *swap_info[MAX_SWAPFILES];
 
 static DEFINE_MUTEX(swapon_mutex);
 
@@ -556,6 +558,7 @@
 			swap_list.next = p->type;
 		nr_swap_pages++;
 		p->inuse_pages--;
+		frontswap_invalidate_page(p->type, offset);
 		if ((p->flags & SWP_BLKDEV) &&
 				disk->fops->swap_slot_free_notify)
 			disk->fops->swap_slot_free_notify(p->bdev, offset);
@@ -985,11 +988,12 @@
 }
 
 /*
- * Scan swap_map from current position to next entry still in use.
+ * Scan swap_map (or frontswap_map if frontswap parameter is true)
+ * from current position to next entry still in use.
  * Recycle to start on reaching the end, returning 0 when empty.
  */
 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
-					unsigned int prev)
+					unsigned int prev, bool frontswap)
 {
 	unsigned int max = si->max;
 	unsigned int i = prev;
@@ -1015,6 +1019,12 @@
 			prev = 0;
 			i = 1;
 		}
+		if (frontswap) {
+			if (frontswap_test(si, i))
+				break;
+			else
+				continue;
+		}
 		count = si->swap_map[i];
 		if (count && swap_count(count) != SWAP_MAP_BAD)
 			break;
@@ -1026,8 +1036,12 @@
  * We completely avoid races by reading each swap page in advance,
  * and then search for the process using it.  All the necessary
  * page table adjustments can then be made atomically.
+ *
+ * if the boolean frontswap is true, only unuse pages_to_unuse pages;
+ * pages_to_unuse==0 means all pages; ignored if frontswap is false
  */
-static int try_to_unuse(unsigned int type)
+int try_to_unuse(unsigned int type, bool frontswap,
+		 unsigned long pages_to_unuse)
 {
 	struct swap_info_struct *si = swap_info[type];
 	struct mm_struct *start_mm;
@@ -1060,7 +1074,7 @@
 	 * one pass through swap_map is enough, but not necessarily:
 	 * there are races when an instance of an entry might be missed.
 	 */
-	while ((i = find_next_to_unuse(si, i)) != 0) {
+	while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
 		if (signal_pending(current)) {
 			retval = -EINTR;
 			break;
@@ -1227,6 +1241,10 @@
 		 * interactive performance.
 		 */
 		cond_resched();
+		if (frontswap && pages_to_unuse > 0) {
+			if (!--pages_to_unuse)
+				break;
+		}
 	}
 
 	mmput(start_mm);
@@ -1486,7 +1504,8 @@
 }
 
 static void enable_swap_info(struct swap_info_struct *p, int prio,
-				unsigned char *swap_map)
+				unsigned char *swap_map,
+				unsigned long *frontswap_map)
 {
 	int i, prev;
 
@@ -1496,6 +1515,7 @@
 	else
 		p->prio = --least_priority;
 	p->swap_map = swap_map;
+	frontswap_map_set(p, frontswap_map);
 	p->flags |= SWP_WRITEOK;
 	nr_swap_pages += p->pages;
 	total_swap_pages += p->pages;
@@ -1512,6 +1532,7 @@
 		swap_list.head = swap_list.next = p->type;
 	else
 		swap_info[prev]->next = p->type;
+	frontswap_init(p->type);
 	spin_unlock(&swap_lock);
 }
 
@@ -1585,7 +1606,7 @@
 	spin_unlock(&swap_lock);
 
 	oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
-	err = try_to_unuse(type);
+	err = try_to_unuse(type, false, 0); /* force all pages to be unused */
 	compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX, oom_score_adj);
 
 	if (err) {
@@ -1596,7 +1617,7 @@
 		 * sys_swapoff for this swap_info_struct at this point.
 		 */
 		/* re-insert swap space back into swap_list */
-		enable_swap_info(p, p->prio, p->swap_map);
+		enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
 		goto out_dput;
 	}
 
@@ -1622,9 +1643,11 @@
 	swap_map = p->swap_map;
 	p->swap_map = NULL;
 	p->flags = 0;
+	frontswap_invalidate_area(type);
 	spin_unlock(&swap_lock);
 	mutex_unlock(&swapon_mutex);
 	vfree(swap_map);
+	vfree(frontswap_map_get(p));
 	/* Destroy swap account informatin */
 	swap_cgroup_swapoff(type);
 
@@ -1988,6 +2011,7 @@
 	sector_t span;
 	unsigned long maxpages;
 	unsigned char *swap_map = NULL;
+	unsigned long *frontswap_map = NULL;
 	struct page *page = NULL;
 	struct inode *inode = NULL;
 
@@ -2071,6 +2095,9 @@
 		error = nr_extents;
 		goto bad_swap;
 	}
+	/* frontswap enabled? set up bit-per-page map for frontswap */
+	if (frontswap_enabled)
+		frontswap_map = vzalloc(maxpages / sizeof(long));
 
 	if (p->bdev) {
 		if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
@@ -2086,14 +2113,15 @@
 	if (swap_flags & SWAP_FLAG_PREFER)
 		prio =
 		  (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
-	enable_swap_info(p, prio, swap_map);
+	enable_swap_info(p, prio, swap_map, frontswap_map);
 
 	printk(KERN_INFO "Adding %uk swap on %s.  "
-			"Priority:%d extents:%d across:%lluk %s%s\n",
+			"Priority:%d extents:%d across:%lluk %s%s%s\n",
 		p->pages<<(PAGE_SHIFT-10), name, p->prio,
 		nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
 		(p->flags & SWP_SOLIDSTATE) ? "SS" : "",
-		(p->flags & SWP_DISCARDABLE) ? "D" : "");
+		(p->flags & SWP_DISCARDABLE) ? "D" : "",
+		(frontswap_map) ? "FS" : "");
 
 	mutex_unlock(&swapon_mutex);
 	atomic_inc(&proc_poll_event);