Re: [RFC PATCH -tip 0/5] perf tools: pagecache monitoring

[Ingo Molnar <mingo@elte.hu>]

* Keiichi KII <k-keiichi@bx.jp.nec.com> wrote:

> 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.

I totally like the approach you have taken here.

Note that tracepoints need a detailed, careful review from interested 
mm folks.

The set of tracepoints does not have to be complete but the 
tracepoints have to be well thought out and near-perfect in this 
context they are instrumenting, with an eye on future extensions with 
the goal of making them painless.

the pagecache tracepoints you have added are:

 include/trace/events/filemap.h |   75 ++++++++++++++++++++++++++++++++++++++++
 mm/filemap.c                   |    4 ++
 mm/truncate.c                  |    2 +
 mm/vmscan.c                    |    2 +
 4 files changed, 83 insertions(+), 0 deletions(-)

So once such kind of review has been iterated through and Andrew et 
al is happy with it i'd be more than happy to dust off the tracing/mm 
bits (which have been done two years ago) and get it all to Linus.

Andrew, Mel, Fengguang?

Thanks,

	Ingo