From: Andrew Morton <akpm@linux-foundation.org>
To: Mel Gorman <mgorman@suse.de>
Cc: Zlatko Calusic <zlatko.calusic@iskon.hr>,
Linus Torvalds <torvalds@linux-foundation.org>,
Hugh Dickins <hughd@google.com>, linux-mm <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: do not sleep in balance_pgdat if there's no i/o congestion
Date: Thu, 20 Dec 2012 12:58:02 -0800 [thread overview]
Message-ID: <20121220125802.23e9b22d.akpm@linux-foundation.org> (raw)
In-Reply-To: <20121220111208.GD10819@suse.de>
On Thu, 20 Dec 2012 11:12:08 +0000
Mel Gorman <mgorman@suse.de> wrote:
> On Thu, Dec 20, 2012 at 12:17:07AM +0100, Zlatko Calusic wrote:
> > On a 4GB RAM machine, where Normal zone is much smaller than
> > DMA32 zone, the Normal zone gets fragmented in time. This requires
> > relatively more pressure in balance_pgdat to get the zone above the
> > required watermark. Unfortunately, the congestion_wait() call in there
> > slows it down for a completely wrong reason, expecting that there's
> > a lot of writeback/swapout, even when there's none (much more common).
> > After a few days, when fragmentation progresses, this flawed logic
> > translates to a very high CPU iowait times, even though there's no
> > I/O congestion at all. If THP is enabled, the problem occurs sooner,
> > but I was able to see it even on !THP kernels, just by giving it a bit
> > more time to occur.
> >
> > The proper way to deal with this is to not wait, unless there's
> > congestion. Thanks to Mel Gorman, we already have the function that
> > perfectly fits the job. The patch was tested on a machine which
> > nicely revealed the problem after only 1 day of uptime, and it's been
> > working great.
> > ---
> > mm/vmscan.c | 12 ++++++------
> > 1 file changed, 6 insertions(+), 6 deletions(-)
> >
>
> Acked-by: Mel Gorman <mgorman@suse.de
There seems to be some complexity/duplication here between the new
unbalanced_zone() and pgdat_balanced().
Can we modify pgdat_balanced() so that it also handles order=0, then do
- if (!unbalanced_zone || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
+ if (!pgdat_balanced(...))
?
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next prev parent reply other threads:[~2012-12-20 20:58 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-19 23:17 [PATCH] mm: do not sleep in balance_pgdat if there's no i/o congestion Zlatko Calusic
2012-12-19 23:25 ` Zlatko Calusic
2012-12-21 11:51 ` Hillf Danton
2012-12-27 15:42 ` Zlatko Calusic
2012-12-29 7:25 ` Hillf Danton
2012-12-29 12:11 ` Zlatko Calusic
2012-12-20 11:12 ` Mel Gorman
2012-12-20 20:58 ` Andrew Morton [this message]
2012-12-22 18:54 ` [PATCH] mm: modify pgdat_balanced() so that it also handles order=0 Zlatko Calusic
2012-12-23 14:12 ` [PATCH v2] " Zlatko Calusic
2012-12-26 15:07 ` [PATCH] mm: avoid calling pgdat_balanced() needlessly Zlatko Calusic
2012-12-28 2:16 ` [PATCH] mm: fix null pointer dereference in wait_iff_congested() Zlatko Calusic
2012-12-28 2:49 ` Minchan Kim
2012-12-28 13:29 ` Zlatko Calusic
2012-12-31 0:50 ` Minchan Kim
2012-12-29 8:45 ` Sedat Dilek
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