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    SubjectRe: [PATCH 4/4] memcg: simplify LRU handling by new rule
    On Wed 21-12-11 09:09:41, KAMEZAWA Hiroyuki wrote:
    > On Tue, 20 Dec 2011 17:16:15 +0100
    > Michal Hocko <mhocko@suse.cz> wrote:
    >
    > > On Wed 14-12-11 16:52:26, KAMEZAWA Hiroyuki wrote:
    > > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > > >
    > > > Now, at LRU handling, memory cgroup needs to do complicated works
    > > > to see valid pc->mem_cgroup, which may be overwritten.
    > > >
    > > > This patch is for relaxing the protocol. This patch guarantees
    > > > - when pc->mem_cgroup is overwritten, page must not be on LRU.
    > >
    > > How the patch guarantees that? I do not see any enforcement. In fact we
    > > depend on the previous patches, don't we.
    > >
    >
    > Ah, yes. We depends on previous patch series.
    >
    >
    > > >
    > > > By this, LRU routine can believe pc->mem_cgroup and don't need to
    > > > check bits on pc->flags. This new rule may adds small overheads to
    > > > swapin. But in most case, lru handling gets faster.
    > > >
    > > > After this patch, PCG_ACCT_LRU bit is obsolete and removed.
    > >
    > > It makes things much more simpler. I just think it needs a better
    > > description.
    > >
    >
    > O.K.
    >
    > 99% of memcg charging are done by following call path.
    >
    > - alloc_page() -> charge() -> map/enter radix-tree -> add to LRU.
    >
    > We need some special case cares.
    >
    > - SwapCache - newly allocated/fully unmapped pages are added to LRU
    > before charge.
    > => handled by previous patch.
    > - FUSE - unused pages are reused.
    > => handled by previous patch.
    >
    > - move_account
    > => we do isolate_page().
    >
    > Now, we can guarantee pc->mem_cgroup is set when page is not added to
    > LRU or under zone->lru_lock + isolate from LRU.
    >
    > I'll add some Documenation to...memcg_debug.txt

    Yes, much better.
    Btw. I forgot to add
    Acked-by: Michal Hocko <mhocko@suse.cz>

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


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