67a5da564f
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>
111 lines
3.7 KiB
Text
111 lines
3.7 KiB
Text
What: /sys/fs/ext4/<disk>/mb_stats
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Date: March 2008
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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Controls whether the multiblock allocator should
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collect statistics, which are shown during the unmount.
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1 means to collect statistics, 0 means not to collect
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statistics
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What: /sys/fs/ext4/<disk>/mb_group_prealloc
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Date: March 2008
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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The multiblock allocator will round up allocation
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requests to a multiple of this tuning parameter if the
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stripe size is not set in the ext4 superblock
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What: /sys/fs/ext4/<disk>/mb_max_to_scan
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Date: March 2008
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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The maximum number of extents the multiblock allocator
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will search to find the best extent
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What: /sys/fs/ext4/<disk>/mb_min_to_scan
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Date: March 2008
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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The minimum number of extents the multiblock allocator
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will search to find the best extent
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What: /sys/fs/ext4/<disk>/mb_order2_req
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Date: March 2008
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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Tuning parameter which controls the minimum size for
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requests (as a power of 2) where the buddy cache is
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used
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What: /sys/fs/ext4/<disk>/mb_stream_req
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Date: March 2008
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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Files which have fewer blocks than this tunable
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parameter will have their blocks allocated out of a
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block group specific preallocation pool, so that small
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files are packed closely together. Each large file
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will have its blocks allocated out of its own unique
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preallocation pool.
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What: /sys/fs/ext4/<disk>/inode_readahead_blks
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Date: March 2008
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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Tuning parameter which controls the maximum number of
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inode table blocks that ext4's inode table readahead
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algorithm will pre-read into the buffer cache
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What: /sys/fs/ext4/<disk>/delayed_allocation_blocks
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Date: March 2008
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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This file is read-only and shows the number of blocks
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that are dirty in the page cache, but which do not
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have their location in the filesystem allocated yet.
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What: /sys/fs/ext4/<disk>/lifetime_write_kbytes
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Date: March 2008
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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This file is read-only and shows the number of kilobytes
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of data that have been written to this filesystem since it was
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created.
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What: /sys/fs/ext4/<disk>/session_write_kbytes
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Date: March 2008
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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This file is read-only and shows the number of
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kilobytes of data that have been written to this
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filesystem since it was mounted.
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What: /sys/fs/ext4/<disk>/inode_goal
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Date: June 2008
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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Tuning parameter which (if non-zero) controls the goal
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inode used by the inode allocator in preference to
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all other allocation heuristics. This is intended for
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debugging use only, and should be 0 on production
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systems.
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What: /sys/fs/ext4/<disk>/max_writeback_mb_bump
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Date: September 2009
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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The maximum number of megabytes the writeback code will
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try to write out before move on to another inode.
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What: /sys/fs/ext4/<disk>/extent_max_zeroout_kb
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Date: August 2012
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Contact: "Theodore Ts'o" <tytso@mit.edu>
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Description:
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The maximum number of kilobytes which will be zeroed
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out in preference to creating a new uninitialized
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extent when manipulating an inode's extent tree. Note
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that using a larger value will increase the
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variability of time necessary to complete a random
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write operation (since a 4k random write might turn
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into a much larger write due to the zeroout
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operation).
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