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Date: Sun, 9 Aug 2009 23:23:51 -0400
From: Theodore Ts'o <tytso@....edu>
To: linux-ext4@...r.kernel.org
Cc: Andreas Dilger <adilger@....com>, Alex Tomas <bzzz@....com>,
Theodore Ts'o <tytso@....edu>
Subject: [PATCH, RFC -V2 0/4] mballoc patches for ext4
This patch series adds better debugging support for mballoc, but the
main goal was to improve how small files are allocated.
These patches could use some testing and benchmarking; I suspect we will
a slight increase the CPU required to read and write small files, but
hopefully it won't be significant enough to be significantly
noticeable. More seriously, the hueristics that try to detect lock
contention and so we go back to using per-cpu group preallocation
extents may need some tuning. We may also want to change the group
preallocation code so that instead of requiring an aligned extent of 512
blocks which is completely unused, that a partially used extent can also
be used for group preallocation.
I used the attached test script, named test-allocate, to demonstrate the
benefits of the last two patches in this patch series. (The first two
simply add better debugging and make the flags field in mb_history
easier to understand.) Without the last two patches applied, the
results of a (bug-fixed) e2freefrag looks like this:
Device: /dev/sdc1
Blocksize: 1024 bytes
Total blocks: 5237156
Free blocks: 5117184 (97.7%)
Min. free extent: 5 KB
Max. free extent: 128992 KB
Avg. free extent: 85286 KB
HISTOGRAM OF FREE EXTENT SIZES:
Chunk Size Range : Free chunks Free Blocks Percent
4K... 8K- : 1 5 0.00%
8K... 16K- : 1 11 0.00%
16K... 32K- : 2 44 0.00%
128K... 256K- : 1 235 0.00%
256K... 512K- : 1 407 0.01%
4M... 8M- : 5 30268 0.59%
8M... 16M- : 5 79723 1.56%
16M... 32M- : 2 46795 0.91%
32M... 64M- : 3 153014 2.99%
64M... 128M- : 39 4806682 93.93%
With the full patch series applied the e2freefrag output looks like
this:
Device: /dev/sdc1
Blocksize: 1024 bytes
Total blocks: 5237156
Free blocks: 5117184 (97.7%)
Min. free extent: 1 KB
Max. free extent: 128992 KB
Avg. free extent: 88227 KB
HISTOGRAM OF FREE EXTENTS SIZES:
Chunk Size Range : Free chunks Free Blocks Percent
1K... 2K- : 2 2 0.00%
2K... 4K- : 1 3 0.00%
4K... 8K- : 1 5 0.00%
4M... 8M- : 5 30268 0.59%
8M... 16M- : 5 80415 1.57%
16M... 32M- : 2 46795 0.91%
32M... 64M- : 3 153014 2.99%
64M... 128M- : 39 4806682 93.93%
Compare the histogram of the sub-megabyte free chunks.
Here is the before output of mb_history:
pid inode original goal result found grps cr flags merge tail broken
1920 513 0/0/1@0 0/0/1@0 0/2371/1@0 1 1 1 0x0000 0 0
398 12 1/0/3@0 0/0/512@0 1/512/512@0 1 1 0 0x04a0 0 0
398 13 1/0/5@0 1/515/5@0
398 14 1/0/7@0 1/520/7@0
398 15 1/0/11@0 1/527/11@0
398 16 1/0/13@0 1/538/13@0
398 17 1/0/15@0 1/551/15@0
398 19 1/0/5@0 1/566/5@0
398 20 1/0/7@0 1/571/7@0
398 21 1/0/11@0 1/578/11@0
398 22 1/0/13@0 1/589/13@0
398 23 1/0/15@0 1/602/15@0
1933 18 1/0/3@0 1/512/512@0 1/1024/512@0 1 1 0 0x04a0 512 1024
398 13 1/0/2@0 1/1027/2@0
398 15 1/0/3@0 1/1029/3@0
398 17 1/0/5@0 1/1032/5@0
398 19 1/0/6@0 1/1037/6@0
398 21 1/0/9@0 1/1043/9@0
398 22 1/0/6@0 1/1052/6@0
398 24 1/0/2@0 1/1058/2@0
398 25 1/0/3@0 1/1060/3@0
398 26 1/0/5@0 1/1063/5@0
398 27 1/0/6@0 1/1068/6@0
398 28 1/0/9@0 1/1074/9@0
398 29 1/0/6@0 1/1083/6@0
.... and here is the after:
pid inode original goal result found grps cr flags merge tail broken
1825 513 0/0/1@0 0/0/1@0 0/2371/1@0 1 1 1 0x0000 0 0
397 12 1/0/3@0 1/0/3@0 1/277/3@0 1 1 1 0x0460 0 0
397 13 1/0/5@0 1/0/5@0 1/280/5@0 9 1 1 0x0460 5 8
397 14 1/0/7@0 1/0/7@0 1/285/7@0 8 1 1 0x0460 4 32
397 15 1/0/11@0 1/0/11@0 1/292/11@0 9 1 1 0x0460 7 8
397 16 1/0/13@0 1/0/13@0 1/303/13@0 8 1 1 0x0460 12 16
397 17 1/0/15@0 1/0/15@0 1/316/15@0 7 1 1 0x0460 11 64
397 18 1/0/3@0 1/0/3@0 1/331/3@0 9 1 1 0x0460 2 4
397 19 1/0/5@0 1/0/5@0 1/334/5@0 8 1 1 0x0460 3 16
397 20 1/0/7@0 1/0/7@0 1/339/7@0 8 1 1 0x0460 2 8
397 21 1/0/11@0 1/0/11@0 1/346/11@0 7 1 1 0x0460 5 32
397 22 1/0/13@0 1/0/13@0 1/357/13@0 7 1 1 0x0460 2 16
397 23 1/0/15@0 1/0/15@0 1/370/15@0 6 1 1 0x0460 1 128
1853 13 1/0/2@0 1/0/2@0 1/300/2@0 1 1 0 0x0460 0 0
1853 15 1/0/3@0 1/0/3@0 1/328/3@0 8 1 1 0x0460 0 0
1853 17 1/0/5@0 1/0/5@0 1/280/5@0 1 1 1 0x0460 0 0
1853 19 1/0/6@0 1/0/6@0 1/346/6@0 5 1 1 0x0460 0 0
1853 21 1/0/9@0 1/0/9@0 1/316/9@0 11 1 1 0x0460 5 8
1853 22 1/0/6@0 1/0/6@0 1/385/6@0 11 1 1 0x0460 3 4
1853 24 1/0/2@0 1/0/2@0 1/326/2@0 1 1 0 0x0460 0 0
1853 25 1/0/3@0 1/0/3@0 1/292/3@0 11 1 1 0x0460 3 4
1853 26 1/0/5@0 1/0/5@0 1/295/5@0 1 1 1 0x0460 0 0
1853 27 1/0/6@0 1/0/6@0 1/391/6@0 11 1 1 0x0460 5 8
1853 28 1/0/9@0 1/0/9@0 1/352/9@0 11 1 1 0x0460 9 16
1853 29 1/0/6@0 1/0/6@0 1/361/6@0 11 1 1 0x0460 3 4
- Ted
------------------------ begin test-allocate
#!/bin/bash
function gen_file()
{
dd if=/dev/zero of=$1 bs=1k count=$2
}
mkdir t
cd t
gen_file a 3
gen_file b 5
gen_file c 7
gen_file d 11
gen_file e 13
gen_file f 15
gen_file g 3
gen_file h 5
gen_file i 7
gen_file j 11
gen_file k 13
gen_file l 15
sync
rm b d f h j k
sync
gen_file m 2
gen_file n 3
gen_file o 5
gen_file p 6
gen_file q 9
gen_file r 6
gen_file s 2
gen_file t 3
gen_file u 5
gen_file v 6
gen_file w 9
gen_file x 6
sync
-------------------------------------------------
Theodore Ts'o (4):
ext4: Add configurable run-time mballoc debugging
ext4: Display the mballoc flags in mb_history in hex instead of
decimal
ext4: Fix bugs in mballoc's stream allocation mode
ext4: Avoid group preallocation for closed files
fs/ext4/Kconfig | 9 ++++
fs/ext4/ext4.h | 46 +++++++++++++++-----
fs/ext4/mballoc.c | 116 ++++++++++++++++++++++++++++++++++++-----------------
fs/ext4/mballoc.h | 16 +++++--
4 files changed, 134 insertions(+), 53 deletions(-)
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