ext4: Don't allow lg prealloc list to be grow large.
Currently, the locality group prealloc list is freed only when there
is a block allocation failure. This can result in large number of
entries in the preallocation list making ext4_mb_use_preallocated()
expensive.
To fix this, we convert the locality group prealloc list to a hash
list. The hash index is the order of number of blocks in the prealloc
space with a max order of 9. When adding prealloc space to the list we
make sure total entries for each order does not exceed 8. If it is
more than 8 we discard few entries and make sure the we have only <= 5
entries.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
index bfe6add..c7c9906 100644
--- a/fs/ext4/mballoc.h
+++ b/fs/ext4/mballoc.h
@@ -164,11 +164,17 @@
* Locality group:
* we try to group all related changes together
* so that writeback can flush/allocate them together as well
+ * Size of lg_prealloc_list hash is determined by MB_DEFAULT_GROUP_PREALLOC
+ * (512). We store prealloc space into the hash based on the pa_free blocks
+ * order value.ie, fls(pa_free)-1;
*/
+#define PREALLOC_TB_SIZE 10
struct ext4_locality_group {
/* for allocator */
- struct mutex lg_mutex; /* to serialize allocates */
- struct list_head lg_prealloc_list;/* list of preallocations */
+ /* to serialize allocates */
+ struct mutex lg_mutex;
+ /* list of preallocations */
+ struct list_head lg_prealloc_list[PREALLOC_TB_SIZE];
spinlock_t lg_prealloc_lock;
};