netdev - [PATCH 1/2] page allocator: Always wake kswapd when restarting an allocation attempt after direct reclaim failed

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Date:	Fri, 16 Oct 2009 11:37:25 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	stable <stable@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	David Miller <davem@...emloft.net>,
	Frans Pop <elendil@...net.nl>,
	reinette chatre <reinette.chatre@...el.com>,
	Kalle Valo <kalle.valo@....fi>,
	"John W. Linville" <linville@...driver.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Karol Lewandowski <karol.k.lewandowski@...il.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"linux-mm@...ck.org\"" <linux-mm@...ck.org>,
	Mel Gorman <mel@....ul.ie>
Subject: [PATCH 1/2] page allocator: Always wake kswapd when restarting an allocation attempt after direct reclaim failed

If a direct reclaim makes no forward progress, it considers whether it
should go OOM or not. Whether OOM is triggered or not, it may retry the
application afterwards. In times past, this would always wake kswapd as well
but currently, kswapd is not woken up after direct reclaim fails. For order-0
allocations, this makes little difference but if there is a heavy mix of
higher-order allocations that direct reclaim is failing for, it might mean
that kswapd is not rewoken for higher orders as much as it did previously.

This patch wakes up kswapd when an allocation is being retried after a direct
reclaim failure. It would be expected that kswapd is already awake, but
this has the effect of telling kswapd to reclaim at the higher order as well.

Signed-off-by: Mel Gorman <mel@....ul.ie>
---
 mm/page_alloc.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bf72055..dfa4362 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1817,9 +1817,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	if (NUMA_BUILD && (gfp_mask & GFP_THISNODE) == GFP_THISNODE)
 		goto nopage;

+restart:
 	wake_all_kswapd(order, zonelist, high_zoneidx);

-restart:
 	/*
 	 * OK, we're below the kswapd watermark and have kicked background
 	 * reclaim. Now things get more complex, so set up alloc_flags according
-- 
1.6.3.3

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