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Date:	Wed, 19 Dec 2012 09:20:09 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Simon Jeons <simon.jeons@...il.com>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/8] mm: memcg: only evict file pages when we have plenty

On Wed, Dec 19, 2012 at 12:21:55AM -0500, Simon Jeons wrote:
> On Mon, 2012-12-17 at 16:54 +0100, Michal Hocko wrote:
> > On Sun 16-12-12 09:21:54, Simon Jeons wrote:
> > > On 12/13/2012 10:55 PM, Michal Hocko wrote:
> > > >On Wed 12-12-12 17:28:44, Johannes Weiner wrote:
> > > >>On Wed, Dec 12, 2012 at 04:53:36PM -0500, Rik van Riel wrote:
> > > >>>On 12/12/2012 04:43 PM, Johannes Weiner wrote:
> > > >>>>dc0422c "mm: vmscan: only evict file pages when we have plenty" makes
> > > >>>>a point of not going for anonymous memory while there is still enough
> > > >>>>inactive cache around.
> > > >>>>
> > > >>>>The check was added only for global reclaim, but it is just as useful
> > > >>>>for memory cgroup reclaim.
> > > >>>>
> > > >>>>Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> > > >>>>---
> > > >>>>  mm/vmscan.c | 19 ++++++++++---------
> > > >>>>  1 file changed, 10 insertions(+), 9 deletions(-)
> > > >>>>
> > > >>>>diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > >>>>index 157bb11..3874dcb 100644
> > > >>>>--- a/mm/vmscan.c
> > > >>>>+++ b/mm/vmscan.c
> > > >>>>@@ -1671,6 +1671,16 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> > > >>>>  		denominator = 1;
> > > >>>>  		goto out;
> > > >>>>  	}
> > > >>>>+	/*
> > > >>>>+	 * There is enough inactive page cache, do not reclaim
> > > >>>>+	 * anything from the anonymous working set right now.
> > > >>>>+	 */
> > > >>>>+	if (!inactive_file_is_low(lruvec)) {
> > > >>>>+		fraction[0] = 0;
> > > >>>>+		fraction[1] = 1;
> > > >>>>+		denominator = 1;
> > > >>>>+		goto out;
> > > >>>>+	}
> > > >>>>
> > > >>>>  	anon  = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
> > > >>>>  		get_lru_size(lruvec, LRU_INACTIVE_ANON);
> > > >>>>@@ -1688,15 +1698,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> > > >>>>  			fraction[1] = 0;
> > > >>>>  			denominator = 1;
> > > >>>>  			goto out;
> > > >>>>-		} else if (!inactive_file_is_low_global(zone)) {
> > > >>>>-			/*
> > > >>>>-			 * There is enough inactive page cache, do not
> > > >>>>-			 * reclaim anything from the working set right now.
> > > >>>>-			 */
> > > >>>>-			fraction[0] = 0;
> > > >>>>-			fraction[1] = 1;
> > > >>>>-			denominator = 1;
> > > >>>>-			goto out;
> > > >>>>  		}
> > > >>>>  	}
> > > >>>>
> > > >>>>
> > > >>>I believe the if() block should be moved to AFTER
> > > >>>the check where we make sure we actually have enough
> > > >>>file pages.
> > > >>You are absolutely right, this makes more sense.  Although I'd figure
> > > >>the impact would be small because if there actually is that little
> > > >>file cache, it won't be there for long with force-file scanning... :-)
> > > >Yes, I think that the result would be worse (more swapping) so the
> > > >change can only help.
> > > >
> > > >>I moved the condition, but it throws conflicts in the rest of the
> > > >>series.  Will re-run tests, wait for Michal and Mel, then resend.
> > > >Yes the patch makes sense for memcg as well. I guess you have tested
> > > >this primarily with memcg. Do you have any numbers? Would be nice to put
> > > >them into the changelog if you have (it should help to reduce swapping
> > > >with heavy streaming IO load).
> > > >
> > > >Acked-by: Michal Hocko <mhocko@...e.cz>
> > > 
> > > Hi Michal,
> > > 
> > > I still can't understand why "The goto out means that it should be
> > > fine either way.",
> > 
> > Not sure I understand your question. goto out just says that either page
> > cache is low or inactive file LRU is too small. And it works for both
> > memcg and global because the page cache is low condition is evaluated
> > only for the global reclaim and always before inactive file is small.
> > Makes more sense?
> 
> Hi Michal,
> 
> I confuse of Gorman's comments below, why the logic change still fine.  
> 

Those comments were wrong.

-- 
Mel Gorman
SUSE Labs
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