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Date: Fri, 12 Mar 2010 13:15:05 +0100 From: Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com> To: Mel Gorman <mel@....ul.ie> CC: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, Nick Piggin <npiggin@...e.de>, Chris Mason <chris.mason@...cle.com>, Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org Subject: Re: [RFC PATCH 0/3] Avoid the use of congestion_wait under zone pressure Mel Gorman wrote: > On Fri, Mar 12, 2010 at 02:05:26AM -0500, Andrew Morton wrote: >> On Fri, 12 Mar 2010 07:39:26 +0100 Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com> wrote: >> >>> >>> Andrew Morton wrote: >>>> On Mon, 8 Mar 2010 11:48:20 +0000 >>>> Mel Gorman <mel@....ul.ie> wrote: [...] >> If not, we broke it again. >> > > We were broken with respect to this in the first place. That > cond_reched() is badly placed and waiting on congestion when congestion > might not be involved is also a bit odd. > > It's possible that Christian's specific problem would also be addressed > by the following patch. Christian, willing to test? Will is here, but no chance before monday/tuesday to get a free machine slot - I'll post results as soon as I get them. > It still feels a bit unnatural though that the page allocator waits on > congestion when what it really cares about is watermarks. Even if this > patch works for Christian, I think it still has merit so will kick it a > few more times. In whatever way I can look at it watermark_wait should be supperior to congestion_wait. Because as Mel points out waiting for watermarks is what is semantically correct there. If there eventually some day comes a solution without any of those waits I'm fine too - e.g. by closing whatever races we have and fixing that one context can never run into this in direct_reclaim: 1. free pages with try_to_free 2. not getting one in the subsequent get_page call But as long as we have a wait - watermark waiting > congestion waiting (IMHO). > ==== CUT HERE ==== > page-allocator: Attempt page allocation immediately after direct reclaim [...] -- GrĂ¼sse / regards, Christian Ehrhardt IBM Linux Technology Center, System z Linux Performance -- 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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