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    SubjectRe: [PATCH] memcg: doc the pagefault count
    On Fri, 4 Nov 2011 17:15:21 +0800
    Wanlong Gao <> wrote:

    > Pagefault count has added to memcg stats since commit 456f998e,
    > but forgot to doc it.
    > Signed-off-by: Wanlong Gao <>
    > ---
    > Documentation/cgroups/memory.txt | 7 +++++++
    > 1 files changed, 7 insertions(+), 0 deletions(-)
    > diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
    > index cc0ebc5..081f4f44 100644
    > --- a/Documentation/cgroups/memory.txt
    > +++ b/Documentation/cgroups/memory.txt
    > @@ -389,6 +389,13 @@ mapped_file - # of bytes of mapped file (includes tmpfs/shmem)
    > pgpgin - # of pages paged in (equivalent to # of charging events).
    > pgpgout - # of pages paged out (equivalent to # of uncharging events).
    > swap - # of bytes of swap usage
    > +
    > +pgfault - # of page-faults
    > +pgmajfault - # of major page-faults
    > + These two are different from "pgpgin"/"pgpgout" stat which
    > + count number of pages charged/discharged to the cgroup and
    > + have no meaning of reading/writing page to disk.
    > +
    > inactive_anon - # of bytes of anonymous memory and swap cache memory on

    OK, but the documentation was already rather poor.

    For a start, what do pgpgin and pgpgout actually count? How about

    pgpgin: the number of pages read from disk as a result of pagefault
    activity within this memcg (swapin and mapped-file pagein). Does not
    include other causes of disk I/O such as read().

    pgpgout: the number of pages written to disk as a result of swap and
    mapped-file activity within this memcg. Does not include other causes
    of disk I/O such as write().

    (I'm really not sure if this is correct!)

    What are the units: is it "pages" or "multiples of 4k"? If the latter
    then userspace must go off and work out what pagesize the kernel is,
    which is a bit ugly and is just asking for people to develop
    monitoring tools which report wrong results on other-than-4k-pagesize

    Once we have that settled then we can move on to documenting pgfault
    and pgmajfault. What are the units? Exactly which kernel actions lead
    to these counters being altered?

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      Last update: 2011-11-09 23:47    [W:0.020 / U:6.028 seconds]
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