Re: [RFC] memcg: handle swapcache leak

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

On Tue, 17 Mar 2009 16:29:50 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Tue, 17 Mar 2009 15:11:13 +0900
> Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> 
> 
> > > Hmm, but IHMO, this is not "leak". "leak" means the object will not be freed forever.
> > > This is a "delay".
> > > 
> > > And I tend to allow this. (stale SwapCache will be on LRU until global LRU found it,
> > > but it's not called leak.)
> > > 
> > You're right, but memcg's reclaim doesn't scan global LRU,
> > so these swapcaches cannot be free'ed by memcg's reclaim.
> > 
> right.
> 
> > This means that a system with memcg's memory pressure but without
> > global memory pressure can use up swap space as swapcaches, doesn't it ?
> > That's what I'm worrying about.
> > 
> This kind of behavior (don't add to LRU if !PageCgroupUsed()) is for swapin-readahead.
> We need this hebavior.
> 
> We never see the swap is exhausted by this issue .....but yes, not 0%.
> 
Just FYI.
I run 5 programs last night, which uses 8MB each, with mem.limit=32M
and 30MB swap on system.
All swap space are used up by swapcache and some programs are oom'ed.


Thanks,
Daisuke Nishimura.

> Without memcg, when the page is added to swap, global LRU runs, anyway.
> With memcg, when the page is added to swap, global LRU will not runs.
> 
> Give me time, I'll find a fix.
> 
> Thanks,
> -Kame
> 

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