From: Mel Gorman <mel@csn.ul.ie>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Shaohua Li <shaohua.li@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@redhat.com>, linux-mm <linux-mm@kvack.org>,
"Chen, Tim C" <tim.c.chen@intel.com>
Subject: Re: too big min_free_kbytes
Date: Thu, 27 Jan 2011 16:03:01 +0000 [thread overview]
Message-ID: <20110127160301.GA29291@csn.ul.ie> (raw)
In-Reply-To: <20110127152755.GB30919@random.random>
On Thu, Jan 27, 2011 at 04:27:55PM +0100, Andrea Arcangeli wrote:
> On Thu, Jan 27, 2011 at 01:40:58PM +0000, Mel Gorman wrote:
> > On Wed, Jan 26, 2011 at 05:42:37PM +0000, Mel Gorman wrote:
> > > On Wed, Jan 26, 2011 at 04:36:55PM +0000, Mel Gorman wrote:
> > > > > But the wmarks don't
> > > > > seem the real offender, maybe it's something related to the tiny pci32
> > > > > zone that materialize on 4g systems that relocate some little memory
> > > > > over 4g to make space for the pci32 mmio. I didn't yet finish to debug
> > > > > it.
> > > > >
> > > >
> > > > This has to be it. What I think is happening is that we're in balance_pgdat(),
> > > > the "Normal" zone is never hitting the watermark and we constantly call
> > > > "goto loop_again" trying to "rebalance" all zones.
> > > >
> > >
> > > Confirmed.
> > > <SNIP>
> >
> > How about the following? Functionally it would work but I am concerned
> > that the logic in balance_pgdat() and kswapd() is getting out of hand
> > having being adjusted to work with a number of corner cases already. In
> > the next cycle, it could do with a "do-over" attempt to make it easier
> > to follow.
>
> That number 8 is the problem,
Agreed, I considered your approach as well. I didn't go with it because it
was the main heuristic that allowed kswapd to skip a zone but still allows
kswapd to keep going. I made the choice to try and put kswapd to sleep
sooner.
> I don't think anybody was ever supposed
> to free 8*highwmark pages. kswapd must work in the hysteresis range
> low->high area and then sleep wait low to hit again before it gets
> wakenup. Not sure how that number 8 ever come up... but to be it looks
> like the real offender and I wouldn't work around it.
>
It was introduced by commit [32a4330d: mm: prevent kswapd from freeing
excessive amounts of lowmem] and sure enough, it was intended to avoid a
situation where memory was freed from every zone if one was imbalanced -
sounds familiar.
> totally untested... I will test....
>
It should work in terms of free memory. When testing, monitor as well if
kswapd is going asleep or if it is stuck in D state. If it's stuck in D state,
it's looping around in balance_pgdat() and consuming CPU for no good reason
(can use vmscan tracepoints to confirm).
--
Mel Gorman
Linux Technology Center
IBM Dublin Software Lab
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next prev parent reply other threads:[~2011-01-27 16:03 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-24 3:56 too big min_free_kbytes Shaohua Li
2011-01-24 15:00 ` Andrea Arcangeli
2011-01-25 14:35 ` Mel Gorman
2011-01-26 14:17 ` Mel Gorman
2011-01-26 15:23 ` Mel Gorman
2011-01-26 15:42 ` Andrea Arcangeli
2011-01-26 16:36 ` Mel Gorman
2011-01-26 17:42 ` Mel Gorman
2011-01-27 13:40 ` Mel Gorman
2011-01-27 15:27 ` Andrea Arcangeli
2011-01-27 16:03 ` Mel Gorman [this message]
2011-01-27 18:52 ` Andrea Arcangeli
2011-01-27 20:33 ` Rik van Riel
2011-01-27 21:31 ` Mel Gorman
2011-01-27 23:18 ` Rik van Riel
2011-01-28 10:35 ` Mel Gorman
2011-01-28 16:28 ` Andrea Arcangeli
2011-01-28 16:46 ` Mel Gorman
2011-01-28 17:16 ` Rik van Riel
2011-01-28 17:46 ` Andrea Arcangeli
2011-01-28 18:03 ` Rik van Riel
2011-01-28 18:24 ` Andrea Arcangeli
2011-01-28 19:34 ` Rik van Riel
2011-01-28 19:45 ` Andrea Arcangeli
2011-01-28 20:55 ` Rik van Riel
2011-01-29 19:45 ` Andrea Arcangeli
2011-01-28 17:34 ` Andrea Arcangeli
2011-01-28 17:10 ` Rik van Riel
2011-02-03 2:58 ` Andrea Arcangeli
2011-02-03 13:15 ` Mel Gorman
2011-02-03 18:59 ` Andrea Arcangeli
2011-02-03 14:36 ` Rik van Riel
2011-02-03 19:11 ` Andrea Arcangeli
2011-02-12 1:28 ` Simon Kirby
2011-02-14 2:25 ` Shaohua Li
2011-02-22 14:25 ` Mel Gorman
2011-02-22 14:42 ` Andrea Arcangeli
2011-02-22 14:50 ` Mel Gorman
2011-02-22 14:54 ` Andrea Arcangeli
2011-02-22 16:04 ` Mel Gorman
2011-02-22 16:40 ` Rik van Riel
2011-02-23 5:29 ` Shaohua Li
2011-02-23 14:45 ` Andrea Arcangeli
2011-02-24 8:08 ` Shaohua Li
2011-02-24 9:52 ` Mel Gorman
2011-02-24 9:57 ` Mel Gorman
2011-02-24 14:27 ` Andrea Arcangeli
2011-02-24 14:04 ` Andrea Arcangeli
2011-02-25 0:51 ` Shaohua Li
2011-02-25 12:13 ` Mel Gorman
2011-02-12 9:48 ` alex shi
2011-02-22 14:24 ` Mel Gorman
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