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    SubjectRe: [PATCH 1/4] memcg: simplify page cache charging.
    On Tue, 20 Dec 2011 13:58:17 -0800
    Andrew Morton <akpm@linux-foundation.org> wrote:

    > On Mon, 19 Dec 2011 09:01:22 +0900
    > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    >
    > > On Fri, 16 Dec 2011 14:28:14 -0800
    > > Andrew Morton <akpm@linux-foundation.org> wrote:
    > >
    > > > On Wed, 14 Dec 2011 16:49:22 +0900
    > > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > > >
    > > > > Because of commit ef6a3c6311, FUSE uses replace_page_cache() instead
    > > > > of add_to_page_cache(). Then, mem_cgroup_cache_charge() is not
    > > > > called against FUSE's pages from splice.
    > > >
    > > > Speaking of ef6a3c6311 ("mm: add replace_page_cache_page() function"),
    > > > may I pathetically remind people that it's rather inefficient?
    > > >
    > > > http://lkml.indiana.edu/hypermail/linux/kernel/1109.1/00375.html
    > > >
    > >
    > > IIRC, people says inefficient because it uses memcg codes for page-migration
    > > for fixing up accounting. Now, We added replace-page-cache for memcg in
    > > memcg-add-mem_cgroup_replace_page_cache-to-fix-lru-issue.patch
    > >
    > > So, I think the problem originally mentioned is fixed.
    > >
    >
    > No, the inefficiency in replace_page_cache_page() is still there. Two
    > identical walks down the radix tree, a pointless decrement then
    > increment of mapping->nrpages, two writes to page->mapping, an often
    > pointless decrement then increment of NR_FILE_PAGES, and probably other things.
    >

    Hmm, then, replace_page_cache_page() itself has some problem.
    I'll look into that.

    Thanks,
    -Kame






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