Re: [RFC] memcg: handle swapcache leak

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

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%.

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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