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authorVivek Haldar <haldar@google.com>2011-05-25 07:41:54 -0400
committerTheodore Ts'o <tytso@mit.edu>2011-05-25 07:41:54 -0400
commit556b27abf73833923d5cd4be80006292e1b31662 (patch)
tree588fa7c3db66afb545921cdfc894f0a41e66dc49 /fs/ext4/ext4.h
parenta4bb6b64e39abc0e41ca077725f2a72c868e7622 (diff)
ext4: do not normalize block requests from fallocate()
Currently, an fallocate request of size slightly larger than a power of 2 is turned into two block requests, each a power of 2, with the extra blocks pre-allocated for future use. When an application calls fallocate, it already has an idea about how large the file may grow so there is usually little benefit to reserve extra blocks on the preallocation list. This reduces disk fragmentation. Tested: fsstress. Also verified manually that fallocat'ed files are contiguously laid out with this change (whereas without it they begin at power-of-2 boundaries, leaving blocks in between). CPU usage of fallocate is not appreciably higher. In a tight fallocate loop, CPU usage hovers between 5%-8% with this change, and 5%-7% without it. Using a simulated file system aging program which the file system to 70%, the percentage of free extents larger than 8MB (as measured by e2freefrag) increased from 38.8% without this change, to 69.4% with this change. Signed-off-by: Vivek Haldar <haldar@google.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to 'fs/ext4/ext4.h')
-rw-r--r--fs/ext4/ext4.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 7bc7c724805d..a74b89c09f90 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -517,6 +517,8 @@ struct ext4_new_group_data {
EXT4_GET_BLOCKS_CREATE_UNINIT_EXT)
/* Punch out blocks of an extent */
#define EXT4_GET_BLOCKS_PUNCH_OUT_EXT 0x0020
+ /* Don't normalize allocation size (used for fallocate) */
+#define EXT4_GET_BLOCKS_NO_NORMALIZE 0x0040
/*
* Flags used by ext4_free_blocks