1What: /sys/fs/ext4/<disk>/mb_stats 2Date: March 2008 3Contact: "Theodore Ts'o" <tytso@mit.edu> 4Description: 5 Controls whether the multiblock allocator should 6 collect statistics, which are shown during the unmount. 7 1 means to collect statistics, 0 means not to collect 8 statistics 9 10What: /sys/fs/ext4/<disk>/mb_group_prealloc 11Date: March 2008 12Contact: "Theodore Ts'o" <tytso@mit.edu> 13Description: 14 The multiblock allocator will round up allocation 15 requests to a multiple of this tuning parameter if the 16 stripe size is not set in the ext4 superblock 17 18What: /sys/fs/ext4/<disk>/mb_max_to_scan 19Date: March 2008 20Contact: "Theodore Ts'o" <tytso@mit.edu> 21Description: 22 The maximum number of extents the multiblock allocator 23 will search to find the best extent 24 25What: /sys/fs/ext4/<disk>/mb_min_to_scan 26Date: March 2008 27Contact: "Theodore Ts'o" <tytso@mit.edu> 28Description: 29 The minimum number of extents the multiblock allocator 30 will search to find the best extent 31 32What: /sys/fs/ext4/<disk>/mb_order2_req 33Date: March 2008 34Contact: "Theodore Ts'o" <tytso@mit.edu> 35Description: 36 Tuning parameter which controls the minimum size for 37 requests (as a power of 2) where the buddy cache is 38 used 39 40What: /sys/fs/ext4/<disk>/mb_stream_req 41Date: March 2008 42Contact: "Theodore Ts'o" <tytso@mit.edu> 43Description: 44 Files which have fewer blocks than this tunable 45 parameter will have their blocks allocated out of a 46 block group specific preallocation pool, so that small 47 files are packed closely together. Each large file 48 will have its blocks allocated out of its own unique 49 preallocation pool. 50 51What: /sys/fs/ext4/<disk>/inode_readahead_blks 52Date: March 2008 53Contact: "Theodore Ts'o" <tytso@mit.edu> 54Description: 55 Tuning parameter which controls the maximum number of 56 inode table blocks that ext4's inode table readahead 57 algorithm will pre-read into the buffer cache 58 59What: /sys/fs/ext4/<disk>/delayed_allocation_blocks 60Date: March 2008 61Contact: "Theodore Ts'o" <tytso@mit.edu> 62Description: 63 This file is read-only and shows the number of blocks 64 that are dirty in the page cache, but which do not 65 have their location in the filesystem allocated yet. 66 67What: /sys/fs/ext4/<disk>/lifetime_write_kbytes 68Date: March 2008 69Contact: "Theodore Ts'o" <tytso@mit.edu> 70Description: 71 This file is read-only and shows the number of kilobytes 72 of data that have been written to this filesystem since it was 73 created. 74 75What: /sys/fs/ext4/<disk>/session_write_kbytes 76Date: March 2008 77Contact: "Theodore Ts'o" <tytso@mit.edu> 78Description: 79 This file is read-only and shows the number of 80 kilobytes of data that have been written to this 81 filesystem since it was mounted. 82 83What: /sys/fs/ext4/<disk>/inode_goal 84Date: June 2008 85Contact: "Theodore Ts'o" <tytso@mit.edu> 86Description: 87 Tuning parameter which (if non-zero) controls the goal 88 inode used by the inode allocator in preference to 89 all other allocation heuristics. This is intended for 90 debugging use only, and should be 0 on production 91 systems. 92 93What: /sys/fs/ext4/<disk>/max_writeback_mb_bump 94Date: September 2009 95Contact: "Theodore Ts'o" <tytso@mit.edu> 96Description: 97 The maximum number of megabytes the writeback code will 98 try to write out before move on to another inode. 99 100What: /sys/fs/ext4/<disk>/extent_max_zeroout_kb 101Date: August 2012 102Contact: "Theodore Ts'o" <tytso@mit.edu> 103Description: 104 The maximum number of kilobytes which will be zeroed 105 out in preference to creating a new uninitialized 106 extent when manipulating an inode's extent tree. Note 107 that using a larger value will increase the 108 variability of time necessary to complete a random 109 write operation (since a 4k random write might turn 110 into a much larger write due to the zeroout 111 operation). 112