From: Johannes Weiner <hannes@cmpxchg.org>
To: Mel Gorman <mgorman@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Linux-FSDevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 6/6] mm: page_alloc: Reduce cost of the fair zone allocation policy
Date: Thu, 10 Jul 2014 08:18:30 -0400 [thread overview]
Message-ID: <20140710121830.GN29639@cmpxchg.org> (raw)
In-Reply-To: <1404893588-21371-7-git-send-email-mgorman@suse.de>
On Wed, Jul 09, 2014 at 09:13:08AM +0100, Mel Gorman wrote:
> The fair zone allocation policy round-robins allocations between zones
> within a node to avoid age inversion problems during reclaim. If the
> first allocation fails, the batch counts is reset and a second attempt
> made before entering the slow path.
>
> One assumption made with this scheme is that batches expire at roughly the
> same time and the resets each time are justified. This assumption does not
> hold when zones reach their low watermark as the batches will be consumed
> at uneven rates. Allocation failure due to watermark depletion result in
> additional zonelist scans for the reset and another watermark check before
> hitting the slowpath.
>
> On UMA, the benefit is negligible -- around 0.25%. On 4-socket NUMA
> machine it's variable due to the variability of measuring overhead with
> the vmstat changes. The system CPU overhead comparison looks like
>
> 3.16.0-rc3 3.16.0-rc3 3.16.0-rc3
> vanilla vmstat-v5 lowercost-v5
> User 746.94 774.56 802.00
> System 65336.22 32847.27 40852.33
> Elapsed 27553.52 27415.04 27368.46
>
> However it is worth noting that the overall benchmark still completed
> faster and intuitively it makes sense to take as few passes as possible
> through the zonelists.
>
> Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
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next prev parent reply other threads:[~2014-07-10 12:18 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-09 8:13 [PATCH 0/5] Reduce sequential read overhead Mel Gorman
2014-07-09 8:13 ` [PATCH 1/6] mm: pagemap: Avoid unnecessary overhead when tracepoints are deactivated Mel Gorman
2014-07-10 12:01 ` Johannes Weiner
2014-07-09 8:13 ` [PATCH 2/6] mm: Rearrange zone fields into read-only, page alloc, statistics and page reclaim lines Mel Gorman
2014-07-10 12:06 ` Johannes Weiner
2014-07-09 8:13 ` [PATCH 3/6] mm: Move zone->pages_scanned into a vmstat counter Mel Gorman
2014-07-10 12:08 ` Johannes Weiner
2014-07-09 8:13 ` [PATCH 4/6] mm: vmscan: Only update per-cpu thresholds for online CPU Mel Gorman
2014-07-10 12:09 ` Johannes Weiner
2014-07-09 8:13 ` [PATCH 5/6] mm: page_alloc: Abort fair zone allocation policy when remotes nodes are encountered Mel Gorman
2014-07-10 12:14 ` Johannes Weiner
2014-07-10 12:44 ` Mel Gorman
2014-07-09 8:13 ` [PATCH 6/6] mm: page_alloc: Reduce cost of the fair zone allocation policy Mel Gorman
2014-07-10 12:18 ` Johannes Weiner [this message]
2014-08-08 15:27 ` Vlastimil Babka
2014-08-11 12:12 ` Mel Gorman
2014-08-11 12:34 ` Vlastimil Babka
2014-09-02 14:01 ` Johannes Weiner
2014-09-05 10:14 ` [PATCH] mm: page_alloc: Fix setting of ZONE_FAIR_DEPLETED on UP Mel Gorman
2014-09-07 6:32 ` Leon Romanovsky
2014-09-08 11:57 ` [PATCH] mm: page_alloc: Fix setting of ZONE_FAIR_DEPLETED on UP v2 Mel Gorman
2014-09-09 8:17 ` Leon Romanovsky
2014-09-09 19:53 ` Andrew Morton
2014-09-10 9:16 ` Mel Gorman
2014-09-10 20:32 ` Johannes Weiner
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