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Date: Tue, 27 Oct 2009 11:42:55 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: David Rientjes <rientjes@...gle.com> Cc: kosaki.motohiro@...fujitsu.com, Mel Gorman <mel@....ul.ie>, Frans Pop <elendil@...net.nl>, Jiri Kosina <jkosina@...e.cz>, Sven Geggus <lists@...hsschwanzdomain.de>, Karol Lewandowski <karol.k.lewandowski@...il.com>, Tobias Oetiker <tobi@...iker.ch>, "Rafael J. Wysocki" <rjw@...k.pl>, David Miller <davem@...emloft.net>, Reinette Chatre <reinette.chatre@...el.com>, Kalle Valo <kalle.valo@....fi>, Mohamed Abbas <mohamed.abbas@...el.com>, Jens Axboe <jens.axboe@...cle.com>, "John W. Linville" <linville@...driver.com>, Pekka Enberg <penberg@...helsinki.fi>, Bartlomiej Zolnierkiewicz <bzolnier@...il.com>, Greg Kroah-Hartman <gregkh@...e.de>, Stephan von Krawczynski <skraw@...net.com>, Kernel Testers List <kernel-testers@...r.kernel.org>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, "linux-mm@...ck.org\"" <linux-mm@...ck.org> Subject: Re: [PATCH 1/5] page allocator: Always wake kswapd when restarting an allocation attempt after direct reclaim failed > On Mon, 26 Oct 2009, KOSAKI Motohiro wrote: > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index bf72055..5a27896 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1899,6 +1899,12 @@ rebalance: > > if (should_alloc_retry(gfp_mask, order, pages_reclaimed)) { > > /* Wait for some write requests to complete then retry */ > > congestion_wait(BLK_RW_ASYNC, HZ/50); > > + > > + /* > > + * While we wait congestion wait, Amount of free memory can > > + * be changed dramatically. Thus, we kick kswapd again. > > + */ > > + wake_all_kswapd(order, zonelist, high_zoneidx); > > goto rebalance; > > } > > > > We're blocking to finish writeback of the directly reclaimed memory, why > do we need to wake kswapd afterwards? the same reason of "goto restart" case. that's my intention. if following scenario occur, it is equivalent that we didn't call wake_all_kswapd(). 1. call congestion_wait() 2. kswapd reclaimed lots memory and sleep 3. another task consume lots memory 4. wakeup from congestion_wait() IOW, if we falled into __alloc_pages_slowpath(), we naturally expect next page_alloc() don't fall into slowpath. however if kswapd end to its work too early, this assumption isn't true. Is this too pessimistic assumption? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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