linux-kernel - Re: [PATCH] vmscan: memcg needs may_swap (Re: [patch] vmscan: rename sc.may_swap to may

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Date:	Wed, 1 Apr 2009 18:03:42 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Rik van Riel <riel@...hat.com>,
	Balbir Singh <balbir@...ibm.com>
Subject: Re: [PATCH] vmscan: memcg needs may_swap (Re: [patch] vmscan: rename  sc.may_swap to may_unmap)

On Wed, Apr 01, 2009 at 06:55:45PM +0900, KOSAKI Motohiro wrote:
> > > > How about making may_swap mean the following:
> > > > 
> > > > 	@@ -642,6 +639,8 @@ static unsigned long shrink_page_list(st
> > > > 	 		 * Try to allocate it some swap space here.
> > > > 	 		 */
> > > > 	 		if (PageAnon(page) && !PageSwapCache(page)) {
> > > > 	+			if (!sc->map_swap)
> > > > 	+				goto keep_locked;
> > > > 	 			if (!(sc->gfp_mask & __GFP_IO))
> > > > 	 				goto keep_locked;
> > > > 	 			if (!add_to_swap(page))
> > > > 
> > > > try_to_free_pages() always sets it.
> > > > 
> > > What is the advantage than _not_ scanning ANON LRU at all ?
> > 
> > I thought we could collect anon pages that don't need swap io.
> 
> Yes. but Is this important?
> if memcg reclaim don't collect sleal swapcache, other global reclaim can.
> 
> Am I missing any viewpoint?

Nothing I am aware of, it should work as you suggest.  I just wasn't
sure about the memory controller.
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