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authorZheng Liu <wenqing.lz@taobao.com>2012-08-17 09:54:17 -0400
committerTheodore Ts'o <tytso@mit.edu>2012-08-17 09:54:17 -0400
commit67a5da564f97f31c4054d358e00b34d7ee570da5 (patch)
tree525f256d46cfac4be0b0acd90cc2bad5fcdb1b77 /Documentation
parent81370291722ac1e0ec95234a0ea91a5bc76b6185 (diff)
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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')
-rw-r--r--Documentation/ABI/testing/sysfs-fs-ext413
1 files changed, 13 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-fs-ext4 b/Documentation/ABI/testing/sysfs-fs-ext4
index f22ac08..c631253 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).
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