From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: mgorman@suse.de
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] mm: page allocator: Initialise ZLC for first zone eligible for zone_reclaim
Date: Wed, 13 Jul 2011 10:15:15 +0900 [thread overview]
Message-ID: <4E1CF1A3.3050401@jp.fujitsu.com> (raw)
In-Reply-To: <1310389274-13995-3-git-send-email-mgorman@suse.de>
(2011/07/11 22:01), Mel Gorman wrote:
> The zonelist cache (ZLC) is used among other things to record if
> zone_reclaim() failed for a particular zone recently. The intention
> is to avoid a high cost scanning extremely long zonelists or scanning
> within the zone uselessly.
>
> 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.
>
> This patch initialises ZLC before the first eligible zone calls
> zone_reclaim(). Once initialised, it is checked whether the zone
> failed zone_reclaim recently. If it has, the zone is skipped. As the
> first zone is now being checked, additional care has to be taken about
> zones marked full. A zone can be marked "full" because it should not
> have enough unmapped pages for zone_reclaim but this is excessive as
> direct reclaim or kswapd may succeed where zone_reclaim fails. Only
> mark zones "full" after zone_reclaim fails if it failed to reclaim
> enough pages after scanning.
>
> Signed-off-by: Mel Gorman <mgorman@suse.de>
If I understand correctly this patch's procs/cons is,
pros.
1) faster when zone reclaim doesn't work effectively
cons.
2) slower when zone reclaim is off
3) slower when zone recliam works effectively
(2) and (3) are frequently happen than (1), correct?
At least, I think we need to keep zero impact when zone reclaim mode is off.
Thanks.
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next prev parent reply other threads:[~2011-07-13 1:15 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-11 13:01 [RFC PATCH 0/3] Reduce frequency of stalls due to zone_reclaim() on NUMA Mel Gorman
2011-07-11 13:01 ` [PATCH 1/3] mm: vmscan: Do use use PF_SWAPWRITE from zone_reclaim Mel Gorman
2011-07-12 9:27 ` Minchan Kim
2011-07-12 9:40 ` KOSAKI Motohiro
2011-07-12 9:55 ` Minchan Kim
2011-07-12 15:43 ` Christoph Lameter
2011-07-13 10:40 ` Mel Gorman
2011-07-12 10:14 ` Mel Gorman
2011-07-13 0:34 ` KOSAKI Motohiro
2011-07-11 13:01 ` [PATCH 2/3] mm: page allocator: Initialise ZLC for first zone eligible for zone_reclaim Mel Gorman
2011-07-13 1:15 ` KOSAKI Motohiro [this message]
2011-07-13 11:02 ` Mel Gorman
2011-07-14 1:20 ` KOSAKI Motohiro
2011-07-14 6:11 ` Mel Gorman
2011-07-11 13:01 ` [PATCH 3/3] mm: page allocator: Reconsider zones for allocation after direct reclaim Mel Gorman
2011-07-13 0:42 ` KOSAKI Motohiro
2011-07-13 11:10 ` Mel Gorman
2011-07-14 3:20 ` KOSAKI Motohiro
2011-07-14 6:10 ` Mel Gorman
2011-07-21 9:35 ` KOSAKI Motohiro
2011-07-21 10:31 ` Mel Gorman
2011-07-15 14:59 [PATCH 0/2] Reduce frequency of stalls due to zone_reclaim() on NUMA v2 Mel Gorman
2011-07-15 14:59 ` [PATCH 2/3] mm: page allocator: Initialise ZLC for first zone eligible for zone_reclaim Mel Gorman
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