From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx132.postini.com [74.125.245.132]) by kanga.kvack.org (Postfix) with SMTP id 131756B0068 for ; Tue, 19 Jun 2012 07:29:33 -0400 (EDT) Received: from epcpsbgm2.samsung.com (mailout1.samsung.com [203.254.224.24]) by mailout1.samsung.com (Oracle Communications Messaging Server 7u4-24.01(7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTP id <0M5V0090P3X47T90@mailout1.samsung.com> for linux-mm@kvack.org; Tue, 19 Jun 2012 20:29:31 +0900 (KST) Received: from bzolnier-desktop.localnet ([106.116.48.38]) by mmp1.samsung.com (Oracle Communications Messaging Server 7u4-24.01 (7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTPA id <0M5V0039A3X6CZ20@mmp1.samsung.com> for linux-mm@kvack.org; Tue, 19 Jun 2012 20:29:31 +0900 (KST) From: Bartlomiej Zolnierkiewicz Subject: Re: [PATCH] cma: cached pageblock type fixup Date: Tue, 19 Jun 2012 13:28:50 +0200 References: <201205230922.00530.b.zolnierkie@samsung.com> <20120619090015.GE20467@suse.de> In-reply-to: <20120619090015.GE20467@suse.de> MIME-version: 1.0 Content-type: Text/Plain; charset=us-ascii Content-transfer-encoding: 7bit Message-id: <201206191328.50781.b.zolnierkie@samsung.com> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: linux-mm@kvack.org, Michal Nazarewicz , Marek Szyprowski On Tuesday 19 June 2012 11:00:15 Mel Gorman wrote: > On Wed, May 23, 2012 at 09:22:00AM +0200, Bartlomiej Zolnierkiewicz wrote: > > From: Bartlomiej Zolnierkiewicz > > Subject: [PATCH] cma: cached pageblock type fixup > > > > CMA pages added to per-cpu pages lists in free_hot_cold_page() > > have private field set to MIGRATE_CMA pageblock type . If this > > happes just before start_isolate_page_range() in alloc_contig_range() > > changes pageblock type of the page to MIGRATE_ISOLATE it may result > > in the cached pageblock type being stale in free_pcppages_bulk() > > (which may be triggered by drain_all_pages() in alloc_contig_range()), > > So what? "page being added to MIGRATE_CMA free list instead of MIGRATE_ISOLATE one in __free_one_page() and (if the page is reused just before test_pages_isolated() check) causing alloc_contig_range() failure." > The pages get freed to the MIGRATE_CMA region. At worst they will be > used for an allocation request that is compatible with being migrated by > CMA. This will delay the allocation time of alloc_contig_range() but is > hardly critical. There is no waiting on MIGRATE_CMA pages in alloc_contig_range() to become free again. If the conversion to MIGRATE_ISOLATE fails then the whole alloc_contig_range() allocation fails on test_pages_isolated() check. > Your fix on the other hand adds another call to get_pageblock_type() to > free_pcppages_bulk which is expensive. The change made to > buffered_rmqueue() is horrific. It takes the per-cpu page allocation > path and adds a spin lock to it which completely defeats the purpose of > having the per-cpu allocation avoid taking locks. This will have a very > heavy impact on performance, particularly on parallel workloads. > > As the impact of the race should be marginal and the cost of the fix is > so unbelivably high I'm nacking this patch. If this race is a problem then > it should be handled in alloc_contig_range() not in the allocator fast paths. Do you have any idea how this race can be handled in alloc_contig_range()? Best regards, -- Bartlomiej Zolnierkiewicz Samsung Poland R&D Center -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org