From: Mel Gorman <mgorman@suse.de>
To: Christoph Lameter <cl@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Minchan Kim <minchan.kim@gmail.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] mm: page allocator: Initialise ZLC for first zone eligible for zone_reclaim
Date: Mon, 18 Jul 2011 17:05:52 +0100 [thread overview]
Message-ID: <20110718160552.GB5349@suse.de> (raw)
In-Reply-To: <alpine.DEB.2.00.1107180951390.30392@router.home>
On Mon, Jul 18, 2011 at 09:56:31AM -0500, Christoph Lameter wrote:
> On Fri, 15 Jul 2011, Mel Gorman wrote:
>
> > Currently the zonelist cache is setup only after the first zone has
> > been considered and zone_reclaim() has been called. The objective was
> > to avoid a costly setup but zone_reclaim is itself quite expensive. If
> > it is failing regularly such as the first eligible zone having mostly
> > mapped pages, the cost in scanning and allocation stalls is far higher
> > than the ZLC initialisation step.
>
> Would it not be easier to set zlc_active and allowednodes based on the
> zone having an active ZLC at the start of get_pages()?
>
What do you mean by a zones active ZLC? zonelists are on a per-node,
not a per-zone basis (see node_zonelist) so a zone doesn't have an
active ZLC as such. If the zlc_active is set at the beginning of
get_page_from_freelist(), it implies that we are calling zlc_setup()
even when the watermarks are met which is unnecessary.
> Buffered_rmqueue is handling the situation of a zone with an ZLC in a
> weird way right now since it ignores the (potentially existing) ZLC
> for the first pass.
Where does buffered_rmqueue() refer to a zonelist_cache?
> zlc_setup() does a lot of things. So that is because
> there is a performance benefit?
>
I do not understand this question. Are you asking if zonelist_cache
has a performance benefit? The answer is "yes" because you can see
how the performance when zone_reclaim degrades when it is not used
for the first zone.
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2011-07-18 16:06 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-15 15:08 [PATCH 0/2] Reduce frequency of stalls due to zone_reclaim() on NUMA v2r1 Mel Gorman
2011-07-15 15:08 ` [PATCH 1/2] mm: page allocator: Initialise ZLC for first zone eligible for zone_reclaim Mel Gorman
2011-07-18 14:56 ` Christoph Lameter
2011-07-18 16:05 ` Mel Gorman [this message]
2011-07-18 17:20 ` Christoph Lameter
2011-07-18 21:13 ` Mel Gorman
2011-07-18 21:54 ` Christoph Lameter
2011-07-19 14:01 ` Christoph Lameter
2011-07-20 18:08 ` Christoph Lameter
2011-07-20 19:18 ` Mel Gorman
2011-07-20 19:28 ` Christoph Lameter
2011-07-20 19:52 ` Christoph Lameter
2011-07-20 21:17 ` Christoph Lameter
2011-07-20 22:48 ` Mel Gorman
2011-07-21 15:24 ` Christoph Lameter
2011-07-15 15:09 ` [PATCH 2/2] mm: page allocator: Reconsider zones for allocation after direct reclaim Mel Gorman
2011-07-19 11:46 ` [PATCH] mm: page allocator: Reconsider zones for allocation after direct reclaim fix Mel Gorman
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