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    Subject[RFC PATCH -tip 0/2 v3] pagecache tracepoints proposal
    Hello,

    This is v3 of a patchset to add some tracepoints for pagecache.

    I would propose several tracepoints for tracing pagecache behavior and
    a script for these.
    By using both the tracepoints and the script, we can analysis pagecache behavior
    like usage or hit ratio with high resolution like per process or per file.
    Example output of the script looks like:

    [process list]
    o yum-3215
    cache find cache hit cache hit
    device inode count count ratio
    --------------------------------------------------------
    253:0 16 34434 34130 99.12%
    253:0 198 9692 9463 97.64%
    253:0 639 647 628 97.06%
    253:0 778 32 29 90.62%
    253:0 7305 50225 49005 97.57%
    253:0 144217 12 10 83.33%
    253:0 262775 16 13 81.25%
    *snip*

    -------------------------------------------------------------------------------

    [file list]
    device cached
    (maj:min) inode pages
    --------------------------------
    253:0 16 5752
    253:0 198 2233
    253:0 639 51
    253:0 778 86
    253:0 7305 12307
    253:0 144217 11
    253:0 262775 39
    *snip*

    [process list]
    o yum-3215
    device cached added removed indirect
    (maj:min) inode pages pages pages removed pages
    ----------------------------------------------------------------
    253:0 16 34130 5752 0 0
    253:0 198 9463 2233 0 0
    253:0 639 628 51 0 0
    253:0 778 29 78 0 0
    253:0 7305 49005 12307 0 0
    253:0 144217 10 11 0 0
    253:0 262775 13 39 0 0
    *snip*
    ----------------------------------------------------------------
    total: 102346 26165 1 0

    We can now know system-wide pagecache usage by /proc/meminfo.
    But we have no method to get higher resolution information like per file or
    per process usage than system-wide one.
    A process may share some pagecache or add a pagecache to the memory or
    remove a pagecache from the memory.
    If a pagecache miss hit ratio rises, maybe it leads to extra I/O and
    affects system performance.

    So, by using the tracepoints we can get the following information.
    1. how many pagecaches each process has per each file
    2. how many pages are cached per each file
    3. how many pagecaches each process shares
    4. how often each process adds/removes pagecache
    5. how long a pagecache stays in the memory
    6. pagecache hit rate per file

    Especially, the monitoring pagecache usage per each file and pagecache hit
    ratio would help us tune some applications like database.
    And it will also help us tune the kernel parameters like "vm.dirty_*".

    Changelog since v2
    o add new script to monitor pagecache hit ratio per process.
    o use DECLARE_EVENT_CLASS

    Changelog since v1
    o Add a script based on "perf trace stream scripting support".

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




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