From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH 3/3] vmscan: Force kswapd to take notice faster when high-order watermarks are being hit Date: Tue, 27 Oct 2009 13:19:05 -0700 Message-ID: <20091027131905.410ec04a.akpm@linux-foundation.org> References: <1256650833-15516-1-git-send-email-mel@csn.ul.ie> <1256650833-15516-4-git-send-email-mel@csn.ul.ie> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1256650833-15516-4-git-send-email-mel@csn.ul.ie> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Mel Gorman Cc: stable@kernel.org, linux-kernel@vger.kernel.org, "linux-mm@kvack.org\"" , Frans Pop , Jiri Kosina , Sven Geggus , Karol Lewandowski , Tobias Oetiker , KOSAKI Motohiro , Pekka Enberg , Rik van Riel , Christoph Lameter , Stephan von Krawczynski , Kernel Testers List , Mel Gorman On Tue, 27 Oct 2009 13:40:33 +0000 Mel Gorman wrote: > When a high-order allocation fails, kswapd is kicked so that it reclaims > at a higher-order to avoid direct reclaimers stall and to help GFP_ATOMIC > allocations. Something has changed in recent kernels that affect the timing > where high-order GFP_ATOMIC allocations are now failing with more frequency, > particularly under pressure. This patch forces kswapd to notice sooner that > high-order allocations are occuring. > "something has changed"? Shouldn't we find out what that is? > --- > mm/vmscan.c | 9 +++++++++ > 1 files changed, 9 insertions(+), 0 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 64e4388..7eceb02 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2016,6 +2016,15 @@ loop_again: > priority != DEF_PRIORITY) > continue; > > + /* > + * Exit the function now and have kswapd start over > + * if it is known that higher orders are required > + */ > + if (pgdat->kswapd_max_order > order) { > + all_zones_ok = 1; > + goto out; > + } > + > if (!zone_watermark_ok(zone, order, > high_wmark_pages(zone), end_zone, 0)) > all_zones_ok = 0; So this handles the case where some concurrent thread or interrupt increases pgdat->kswapd_max_order while kswapd was running balance_pgdat(), yes? Does that actually happen much? Enough for this patch to make any useful difference? If one where to whack a printk in that `if' block, how often would it trigger, and under what circumstances? If the -stable maintainers were to ask me "why did you send this" then right now my answer would have to be "I have no idea". Help.