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Subject[RFC PATCH -tip 0/5] perf tools: pagecache monitoring
Hello,

I would propose pagecache monitoring tools using perf tools.
The purpose of the tools is to clarify pagecache behavior in a system.

We can now know system-wide pagecache usage by "/proc/meminfo".
But we don't have any way to get higher resolution information like
per file or per process usage than system-wide one.
If pagecache miss hit ratio rises due to unnecessary adding/removing
pagecaches, maybe it leads to extra I/O and affects system performance.
But it's difficult to find out what is going on in the system.

So, the tools I propose provide 2 functions:

1. pagecache snapshooting(perf script pagecache-snapshoot)

This function clarifies pagecache usage per each file in the system.
This function is based mainly on "pagecache object collections" that is
developed by Wu Fengguang (http://lkml.org/lkml/2010/2/9/156).
The following is sample output of this function.

pagecache snapshooting (time: 14131, path: /home)
file name cache(B) file(B) ratio +/-(B) age
-------------------------------------- -------- -------- ------ ------- ------
/home/foo/git/linux-2.6-tip/.git/objec 71.0M 436.6M 16% 0 9012
/home/foo/git/linux-2.6-tip/.git/objec 49.6M 57.7M 86% 0 9012
/home/foo/.thunderbird/xso5zn7g.defaul 19.8M 19.8M 100% 0 7223
/home/foo/.thunderbird/xso5zn7g.defaul 5.7M 5.7M 100% 0 6621
/home/foo/git/linux-2.6-tip/.git/index 3.5M 3.5M 100% 0 4306
/home/foo/.thunderbird/xso5zn7g.defaul 2.2M 2.2M 100% 0 7524
/home/foo/.thunderbird/xso5zn7g.defaul 2.2M 2.2M 100% 0 7526
/home/foo/.thunderbird/xso5zn7g.defaul 1.7M 1.7M 100% 0 6921
...

2. continuous pagecache monitoring(perf script pagecachetop)

This function clarifies pagecache behavior like pagecache hit ratio and
added/removed pagecache amount on the basis of file/process.
This functions is based on pagecache tracepoints I propose.
While the pagecache snapshooting can take a pagecache snapshoot at a point,
the continuous pagecache monitoring can measure dynamic change between
2 snapshoots.
The following is sample output of this function.

pagecache behavior per file (time:15826, interval:10)

find hit cache add remove proc
file count ratio pages(B) pages(B) pages(B) count
-------------------- -------- ---------- -------- -------- -------- -----
libc-2.13.so 620 100.00% 1.2M 0 0 7
bash 283 100.00% 888.0K 0 0 6
ld-2.13.so 136 100.00% 148.0K 0 0 6
gawk 130 100.00% 376.0K 0 0 2
ld.so.cache 60 100.00% 116.0K 0 0 4
...

pagecache behavior per process (time:16294, interval:10)

find hit add remove file
process count ratio pages(B) pages(B) count
-------------------- -------- ---------- -------- -------- -----
zsh-7761 2968 99.93% 4.0K 0 246
perf-7758 369 100.00% 0 0 17
xmms-7634 52 100.00% 0 0 1
perf-7759 11 100.00% 0 0 2
zsh-2815 6 83.33% 4.0K 4.0K 2
gconfd-2-4849 3 0.00% 12.0K 12.0K 4
rsyslogd-7194 1 100.00% 0 0 1


By these 2 functions, we can find out whether pagecaches are used
efficiently or not.
And also these tools would help us tune some applications like database.
It will also help us tune the kernel parameters like "vm.dirty_*".

My patches are based on the latest "linux-tip.git" tree and
also the following 3 commits in "tip:tracing/mm" and a "pagecache
object collections" patch.

- dcac8cd: tracing/mm: add page frame snapshot trace
- 1487a7a: tracing/mm: fix mapcount trace record field
- eb46710: tracing/mm: rename 'trigger' file to 'dump_range'
- http://lkml.org/lkml/2010/2/9/156

Any comments are welcome.
--
Keiichi Kii <k-keiichi@bx.jp.nec.com>




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