Re: [PATCH 4/4] memcg: simplify LRU handling by new rule

Michal Hocko
2011-12-21T06:56:16Z

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 After this patch, PCG_ACCT_LRU bit is obsolete and removed.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.
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Czech Republic