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| author |   Zheng Liu <wenqing.lz@taobao.com> | 2012-08-17 09:54:17 -0400 |
|---|---|---|
| committer |   Theodore Ts'o <tytso@mit.edu> | 2012-08-17 09:54:17 -0400 |
| commit | 67a5da564f97f31c4054d358e00b34d7ee570da5 (patch) | |
| tree | 525f256d46cfac4be0b0acd90cc2bad5fcdb1b77 /Documentation/ABI | |
| parent | ext4: add missing space to trace message (diff) | |
| download | linux-dev-67a5da564f97f31c4054d358e00b34d7ee570da5.tar.xz linux-dev-67a5da564f97f31c4054d358e00b34d7ee570da5.zip | |
ext4: make the zero-out chunk size tunable
Currently in ext4 the length of zero-out chunk is set to 7 file system
blocks. But if an inode has uninitailized extents from using
fallocate to preallocate space, and the workload issues many random
writes, this can cause a fragmented extent tree that will
unnecessarily grow the extent tree.
So create a new sysfs tunable, extent_max_zeroout_kb, which controls
the maximum size where blocks will be zeroed out instead of creating a
new uninitialized extent. The default of this has been sent to 32kb.
CC: Zach Brown <zab@zabbo.net>
CC: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to 'Documentation/ABI')
| -rw-r--r-- | Documentation/ABI/testing/sysfs-fs-ext4 | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-fs-ext4 b/Documentation/ABI/testing/sysfs-fs-ext4 index f22ac0872ae8..c631253cf85c 100644 --- a/Documentation/ABI/testing/sysfs-fs-ext4 +++ b/Documentation/ABI/testing/sysfs-fs-ext4 @@ -96,3 +96,16 @@ Contact: "Theodore Ts'o" <tytso@mit.edu> Description: The maximum number of megabytes the writeback code will try to write out before move on to another inode. + +What: /sys/fs/ext4/<disk>/extent_max_zeroout_kb +Date: August 2012 +Contact: "Theodore Ts'o" <tytso@mit.edu> +Description: + The maximum number of kilobytes which will be zeroed + out in preference to creating a new uninitialized + extent when manipulating an inode's extent tree. Note + that using a larger value will increase the + variability of time necessary to complete a random + write operation (since a 4k random write might turn + into a much larger write due to the zeroout + operation). |