ksm: separate stable_node
Though we still do well to keep rmap_items in the unstable tree without a
separate tree_item at the node, for several reasons it becomes awkward to
keep rmap_items in the stable tree without a separate stable_node: lack of
space in the nicely-sized rmap_item, the need for an anchor as rmap_items
are removed, the need for a node even when temporarily no rmap_items are
attached to it.
So declare struct stable_node (rb_node to place it in the tree and
hlist_head for the rmap_items hanging off it), and convert stable tree
handling to use it: without yet taking advantage of it. Note how one
stable_tree_insert() of a node now has _two_ stable_tree_append()s of the
two rmap_items being merged.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/ksm.c b/mm/ksm.c
index e8e9a2b..9b7af2e 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -106,34 +106,44 @@
};
/**
+ * struct stable_node - node of the stable rbtree
+ * @node: rb node of this ksm page in the stable tree
+ * @hlist: hlist head of rmap_items using this ksm page
+ */
+struct stable_node {
+ struct rb_node node;
+ struct hlist_head hlist;
+};
+
+/**
* struct rmap_item - reverse mapping item for virtual addresses
* @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
* @filler: unused space we're making available in this patch
* @mm: the memory structure this rmap_item is pointing into
* @address: the virtual address this rmap_item tracks (+ flags in low bits)
* @oldchecksum: previous checksum of the page at that virtual address
- * @node: rb_node of this rmap_item in either unstable or stable tree
- * @next: next rmap_item hanging off the same node of the stable tree
- * @prev: previous rmap_item hanging off the same node of the stable tree
+ * @node: rb node of this rmap_item in the unstable tree
+ * @head: pointer to stable_node heading this list in the stable tree
+ * @hlist: link into hlist of rmap_items hanging off that stable_node
*/
struct rmap_item {
struct rmap_item *rmap_list;
unsigned long filler;
struct mm_struct *mm;
unsigned long address; /* + low bits used for flags below */
+ unsigned int oldchecksum; /* when unstable */
union {
- unsigned int oldchecksum; /* when unstable */
- struct rmap_item *next; /* when stable */
- };
- union {
- struct rb_node node; /* when tree node */
- struct rmap_item *prev; /* in stable list */
+ struct rb_node node; /* when node of unstable tree */
+ struct { /* when listed from stable tree */
+ struct stable_node *head;
+ struct hlist_node hlist;
+ };
};
};
#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
-#define NODE_FLAG 0x100 /* is a node of unstable or stable tree */
-#define STABLE_FLAG 0x200 /* is a node or list item of stable tree */
+#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
+#define STABLE_FLAG 0x200 /* is listed from the stable tree */
/* The stable and unstable tree heads */
static struct rb_root root_stable_tree = RB_ROOT;
@@ -150,6 +160,7 @@
};
static struct kmem_cache *rmap_item_cache;
+static struct kmem_cache *stable_node_cache;
static struct kmem_cache *mm_slot_cache;
/* The number of nodes in the stable tree */
@@ -192,13 +203,19 @@
if (!rmap_item_cache)
goto out;
+ stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
+ if (!stable_node_cache)
+ goto out_free1;
+
mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
if (!mm_slot_cache)
- goto out_free;
+ goto out_free2;
return 0;
-out_free:
+out_free2:
+ kmem_cache_destroy(stable_node_cache);
+out_free1:
kmem_cache_destroy(rmap_item_cache);
out:
return -ENOMEM;
@@ -207,6 +224,7 @@
static void __init ksm_slab_free(void)
{
kmem_cache_destroy(mm_slot_cache);
+ kmem_cache_destroy(stable_node_cache);
kmem_cache_destroy(rmap_item_cache);
mm_slot_cache = NULL;
}
@@ -228,6 +246,16 @@
kmem_cache_free(rmap_item_cache, rmap_item);
}
+static inline struct stable_node *alloc_stable_node(void)
+{
+ return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
+}
+
+static inline void free_stable_node(struct stable_node *stable_node)
+{
+ kmem_cache_free(stable_node_cache, stable_node);
+}
+
static inline struct mm_slot *alloc_mm_slot(void)
{
if (!mm_slot_cache) /* initialization failed */
@@ -429,36 +457,22 @@
*/
static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
{
- if (in_stable_tree(rmap_item)) {
- struct rmap_item *next_item = rmap_item->next;
+ if (rmap_item->address & STABLE_FLAG) {
+ struct stable_node *stable_node;
- if (rmap_item->address & NODE_FLAG) {
- if (next_item) {
- rb_replace_node(&rmap_item->node,
- &next_item->node,
- &root_stable_tree);
- next_item->address |= NODE_FLAG;
- ksm_pages_sharing--;
- } else {
- rb_erase(&rmap_item->node, &root_stable_tree);
- ksm_pages_shared--;
- }
- } else {
- struct rmap_item *prev_item = rmap_item->prev;
-
- BUG_ON(prev_item->next != rmap_item);
- prev_item->next = next_item;
- if (next_item) {
- BUG_ON(next_item->prev != rmap_item);
- next_item->prev = rmap_item->prev;
- }
+ stable_node = rmap_item->head;
+ hlist_del(&rmap_item->hlist);
+ if (stable_node->hlist.first)
ksm_pages_sharing--;
+ else {
+ rb_erase(&stable_node->node, &root_stable_tree);
+ free_stable_node(stable_node);
+ ksm_pages_shared--;
}
- rmap_item->next = NULL;
rmap_item->address &= PAGE_MASK;
- } else if (rmap_item->address & NODE_FLAG) {
+ } else if (rmap_item->address & UNSTABLE_FLAG) {
unsigned char age;
/*
* Usually ksmd can and must skip the rb_erase, because
@@ -859,31 +873,32 @@
* This function checks if there is a page inside the stable tree
* with identical content to the page that we are scanning right now.
*
- * This function return rmap_item pointer to the identical item if found,
+ * This function returns the stable tree node of identical content if found,
* NULL otherwise.
*/
-static struct rmap_item *stable_tree_search(struct page *page,
- struct page **tree_pagep)
+static struct stable_node *stable_tree_search(struct page *page,
+ struct page **tree_pagep)
{
struct rb_node *node = root_stable_tree.rb_node;
+ struct stable_node *stable_node;
while (node) {
- struct rmap_item *tree_rmap_item, *next_rmap_item;
+ struct hlist_node *hlist, *hnext;
+ struct rmap_item *tree_rmap_item;
struct page *tree_page;
int ret;
- tree_rmap_item = rb_entry(node, struct rmap_item, node);
- while (tree_rmap_item) {
+ stable_node = rb_entry(node, struct stable_node, node);
+ hlist_for_each_entry_safe(tree_rmap_item, hlist, hnext,
+ &stable_node->hlist, hlist) {
BUG_ON(!in_stable_tree(tree_rmap_item));
cond_resched();
tree_page = get_ksm_page(tree_rmap_item);
if (tree_page)
break;
- next_rmap_item = tree_rmap_item->next;
remove_rmap_item_from_tree(tree_rmap_item);
- tree_rmap_item = next_rmap_item;
}
- if (!tree_rmap_item)
+ if (!hlist)
return NULL;
ret = memcmp_pages(page, tree_page);
@@ -896,7 +911,7 @@
node = node->rb_right;
} else {
*tree_pagep = tree_page;
- return tree_rmap_item;
+ return stable_node;
}
}
@@ -907,31 +922,32 @@
* stable_tree_insert - insert rmap_item pointing to new ksm page
* into the stable tree.
*
- * This function returns rmap_item if success, NULL otherwise.
+ * This function returns the stable tree node just allocated on success,
+ * NULL otherwise.
*/
-static struct rmap_item *stable_tree_insert(struct page *kpage,
- struct rmap_item *rmap_item)
+static struct stable_node *stable_tree_insert(struct page *kpage)
{
struct rb_node **new = &root_stable_tree.rb_node;
struct rb_node *parent = NULL;
+ struct stable_node *stable_node;
while (*new) {
- struct rmap_item *tree_rmap_item, *next_rmap_item;
+ struct hlist_node *hlist, *hnext;
+ struct rmap_item *tree_rmap_item;
struct page *tree_page;
int ret;
- tree_rmap_item = rb_entry(*new, struct rmap_item, node);
- while (tree_rmap_item) {
+ stable_node = rb_entry(*new, struct stable_node, node);
+ hlist_for_each_entry_safe(tree_rmap_item, hlist, hnext,
+ &stable_node->hlist, hlist) {
BUG_ON(!in_stable_tree(tree_rmap_item));
cond_resched();
tree_page = get_ksm_page(tree_rmap_item);
if (tree_page)
break;
- next_rmap_item = tree_rmap_item->next;
remove_rmap_item_from_tree(tree_rmap_item);
- tree_rmap_item = next_rmap_item;
}
- if (!tree_rmap_item)
+ if (!hlist)
return NULL;
ret = memcmp_pages(kpage, tree_page);
@@ -952,13 +968,16 @@
}
}
- rmap_item->address |= NODE_FLAG | STABLE_FLAG;
- rmap_item->next = NULL;
- rb_link_node(&rmap_item->node, parent, new);
- rb_insert_color(&rmap_item->node, &root_stable_tree);
+ stable_node = alloc_stable_node();
+ if (!stable_node)
+ return NULL;
- ksm_pages_shared++;
- return rmap_item;
+ rb_link_node(&stable_node->node, parent, new);
+ rb_insert_color(&stable_node->node, &root_stable_tree);
+
+ INIT_HLIST_HEAD(&stable_node->hlist);
+
+ return stable_node;
}
/*
@@ -1018,7 +1037,7 @@
}
}
- rmap_item->address |= NODE_FLAG;
+ rmap_item->address |= UNSTABLE_FLAG;
rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
rb_link_node(&rmap_item->node, parent, new);
rb_insert_color(&rmap_item->node, &root_unstable_tree);
@@ -1033,18 +1052,16 @@
* the same ksm page.
*/
static void stable_tree_append(struct rmap_item *rmap_item,
- struct rmap_item *tree_rmap_item)
+ struct stable_node *stable_node)
{
- rmap_item->next = tree_rmap_item->next;
- rmap_item->prev = tree_rmap_item;
-
- if (tree_rmap_item->next)
- tree_rmap_item->next->prev = rmap_item;
-
- tree_rmap_item->next = rmap_item;
+ rmap_item->head = stable_node;
rmap_item->address |= STABLE_FLAG;
+ hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
- ksm_pages_sharing++;
+ if (rmap_item->hlist.next)
+ ksm_pages_sharing++;
+ else
+ ksm_pages_shared++;
}
/*
@@ -1060,6 +1077,7 @@
{
struct rmap_item *tree_rmap_item;
struct page *tree_page = NULL;
+ struct stable_node *stable_node;
struct page *kpage;
unsigned int checksum;
int err;
@@ -1067,8 +1085,8 @@
remove_rmap_item_from_tree(rmap_item);
/* We first start with searching the page inside the stable tree */
- tree_rmap_item = stable_tree_search(page, &tree_page);
- if (tree_rmap_item) {
+ stable_node = stable_tree_search(page, &tree_page);
+ if (stable_node) {
kpage = tree_page;
if (page == kpage) /* forked */
err = 0;
@@ -1080,7 +1098,7 @@
* The page was successfully merged:
* add its rmap_item to the stable tree.
*/
- stable_tree_append(rmap_item, tree_rmap_item);
+ stable_tree_append(rmap_item, stable_node);
}
put_page(kpage);
return;
@@ -1121,19 +1139,23 @@
if (kpage) {
remove_rmap_item_from_tree(tree_rmap_item);
+ stable_node = stable_tree_insert(kpage);
+ if (stable_node) {
+ stable_tree_append(tree_rmap_item, stable_node);
+ stable_tree_append(rmap_item, stable_node);
+ }
+ put_page(kpage);
+
/*
* If we fail to insert the page into the stable tree,
* we will have 2 virtual addresses that are pointing
* to a ksm page left outside the stable tree,
* in which case we need to break_cow on both.
*/
- if (stable_tree_insert(kpage, tree_rmap_item))
- stable_tree_append(rmap_item, tree_rmap_item);
- else {
+ if (!stable_node) {
break_cow(tree_rmap_item);
break_cow(rmap_item);
}
- put_page(kpage);
}
}
}