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    SubjectRe: [PATCH] memcg: handle shmem's swap cache (Was 2.6.26-rc8-mm1
    On Sat, 05 Jul 2008 11:11:10 +0530
    Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

    > KAMEZAWA Hiroyuki wrote:
    > > My swapcache accounting under memcg patch failed to catch tmpfs(shmem)'s one.
    > > Can I test this under -mm tree ?
    > > (If -mm is busy, I'm not in hurry.)
    > > This patch works well in my box.
    > > =
    > > SwapCache handling fix.
    > >
    > > shmem's swapcache behavior is a little different from anonymous's one and
    > > memcg failed to handle it. This patch tries to fix it.
    > >
    > > After this:
    > >
    > > Any page marked as SwapCache is not uncharged. (delelte_from_swap_cache()
    > > delete the SwapCache flag.)
    > >
    > > To check a shmem-page-cache is alive or not we use
    > > page->mapping && !PageAnon(page) instead of
    > > pc->flags & PAGE_CGROUP_FLAG_CACHE.
    > >
    > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    >
    > Though I am not opposed to this, I do sit up and think if keeping the reference
    > count around could avoid this complexity and from my point, the maintenance
    > overhead of this logic/code (I fear there might be more special cases :( )

    yes, to me. but we have to fix..

    But I don't like old code's refcnt handling which does
    - increment
    - does this increment was really neccesary ?
    No? ok, decrement it again.

    This was much more complex to me than current code.

    And old ones will needs the check at treating swap-cache. (it couldn't but if we want)

    >
    > The trade-off is complexity versus the overhead of reference counting.
    >
    refcnt was also very complex ;)

    Thanks,
    -Kame

    > --
    > Warm Regards,
    > Balbir Singh
    > Linux Technology Center
    > IBM, ISTL
    >



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