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    SubjectRe: [patch 03/11] mm: shmem: do not try to uncharge known swapcache pages
    On Mon 09-07-12 13:37:39, Hugh Dickins wrote:
    > On Mon, 9 Jul 2012, Michal Hocko wrote:
    > >
    > > Maybe I am missing something but who does the uncharge from:
    > > shmem_unuse
    > > mem_cgroup_cache_charge
    > > shmem_unuse_inode
    > > shmem_add_to_page_cache
    >
    > There isn't any special uncharge for shmem_unuse(): once the swapcache
    > page is matched up with its memcg, it will get uncharged by one of the
    > usual routes to swapcache_free() when the page is freed: maybe in the
    > call from __remove_mapping(), maybe when free_page_and_swap_cache()
    > ends up calling it.
    >
    > Perhaps you're worrying about error (or unfound) paths in shmem_unuse()?

    Yes that was exactly my concern.

    > By the time we make the charge, we know for sure that it's a shmem page,
    > and make the charge appropriately; in racy cases it might get uncharged
    > again in the delete_from_swap_cache(). Can the unfound case occur these
    > days?

    I cannot find a change that would prevent from that.

    > I'd have to think more deeply to answer that, but the charge will
    > not go missing.
    >
    > Hugh

    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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