Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754009AbaFYB6R (ORCPT ); Tue, 24 Jun 2014 21:58:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40072 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753648AbaFYB6O (ORCPT ); Tue, 24 Jun 2014 21:58:14 -0400 Date: Tue, 24 Jun 2014 21:57:33 -0400 From: Naoya Horiguchi To: Vlastimil Babka Cc: linux-mm@kvack.org, Andrew Morton , David Rientjes , Minchan Kim , Mel Gorman , Joonsoo Kim , Michal Nazarewicz , Christoph Lameter , Rik van Riel , Zhang Yanfei , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 12/13] mm, compaction: try to capture the just-created high-order freepage Message-ID: <20140625015733.GC12855@nhori.redhat.com> References: <1403279383-5862-1-git-send-email-vbabka@suse.cz> <1403279383-5862-13-git-send-email-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1403279383-5862-13-git-send-email-vbabka@suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 20, 2014 at 05:49:42PM +0200, Vlastimil Babka wrote: > Compaction uses watermark checking to determine if it succeeded in creating > a high-order free page. My testing has shown that this is quite racy and it > can happen that watermark checking in compaction succeeds, and moments later > the watermark checking in page allocation fails, even though the number of > free pages has increased meanwhile. > > It should be more reliable if direct compaction captured the high-order free > page as soon as it detects it, and pass it back to allocation. This would > also reduce the window for somebody else to allocate the free page. > > Capture has been implemented before by 1fb3f8ca0e92 ("mm: compaction: capture > a suitable high-order page immediately when it is made available"), but later > reverted by 8fb74b9f ("mm: compaction: partially revert capture of suitable > high-order page") due to a bug. > > This patch differs from the previous attempt in two aspects: > > 1) The previous patch scanned free lists to capture the page. In this patch, > only the cc->order aligned block that the migration scanner just finished > is considered, but only if pages were actually isolated for migration in > that block. Tracking cc->order aligned blocks also has benefits for the > following patch that skips blocks where non-migratable pages were found. > > 2) The operations done in buffered_rmqueue() and get_page_from_freelist() are > closely followed so that page capture mimics normal page allocation as much > as possible. This includes operations such as prep_new_page() and > page->pfmemalloc setting (that was missing in the previous attempt), zone > statistics are updated etc. Due to subtleties with IRQ disabling and > enabling this cannot be simply factored out from the normal allocation > functions without affecting the fastpath. > > This patch has tripled compaction success rates (as recorded in vmstat) in > stress-highalloc mmtests benchmark, although allocation success rates increased > only by a few percent. Closer inspection shows that due to the racy watermark > checking and lack of lru_add_drain(), the allocations that resulted in direct > compactions were often failing, but later allocations succeeeded in the fast > path. So the benefit of the patch to allocation success rates may be limited, > but it improves the fairness in the sense that whoever spent the time > compacting has a higher change of benefitting from it, and also can stop > compacting sooner, as page availability is detected immediately. With better > success detection, the contribution of compaction to high-order allocation > success success rates is also no longer understated by the vmstats. > > Signed-off-by: Vlastimil Babka > Cc: Minchan Kim > Cc: Mel Gorman > Cc: Joonsoo Kim > Cc: Michal Nazarewicz > Cc: Naoya Horiguchi > Cc: Christoph Lameter > Cc: Rik van Riel > Cc: David Rientjes > --- ... > @@ -669,6 +708,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc, > continue; > if (PageTransHuge(page)) { > low_pfn += (1 << compound_order(page)) - 1; > + next_capture_pfn = low_pfn + 1; Don't we need if (next_capture_pfn) here? Thanks, Naoya Horiguchi > continue; > } > } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/