Re: [PATCH] fix unused/stale swap cache handling on memcg v3

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

On Fri, 17 Apr 2009 16:58:06 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Fri, 17 Apr 2009 16:50:36 +0900
> Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> 
> > On Fri, 17 Apr 2009 15:54:11 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > > On Fri, 17 Apr 2009 15:34:55 +0900
> > > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> > > > I made a patch for reclaiming SwapCache from orphan LRU based on your patch,
> > > > and have been testing it these days.
> > > > 
> > > Good trial! 
> > > Honestly, I've written a patch to fix this problem in these days but seems to
> > > be over-kill ;)
> > > 
> > > 
> > > > Major changes from your version:
> > > > - count the number of orphan pages per zone and make the threshold per zone(4MB).
> > > > - As for type 2 of orphan SwapCache, they are usually set dirty by add_to_swap.
> > > >   But try_to_drop_swapcache(__remove_mapping) can't free dirty pages,
> > > >   so add a check and try_to_free_swap to the end of shrink_page_list.
> > > > 
> > > > It seems work fine, no "pseud leak" of SwapCache can be seen.
> > > > 
> > > > What do you think ?
> > > > If it's all right, I'll merge this with the orphan list framework patch
> > > > and send it to Andrew with other fixes of memcg that I have.
> > > > 
> > > I'm sorry but my answer is "please wait". The reason is..
> > > 
> > > 1. When global LRU works, the pages will be reclaimed.
> > > 2. Global LRU will work finally.
> > > 3. While testing, "stale" swap cache cannot be big amount.
> > > 
> > Hmm, I can't understand 2.
> > 
> > If (memsize on system) >> (swapsize on system), global LRU doesn't run
> > and all the swap space can be used up by these SwapCache.
> > This means setting mem.limit can use up all the swap space on the system.
> > I've tested with 50MB size of swap and it can be used up in less than 24h.
> > I think it's not small.
> > 
> 
> plz add hook to shrink_zone() to fix this as you did. 
> orphan list is overkilling at this stage.
> 
I see.

I'll make a patch, test it, and repost it in next week.
It can prevent at least type-2 of orphan SwapCache.

I'll revisit orphan list if needed in future.


Thanks,
Daisuke Nishimura.

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