Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751257AbbG2J7Z (ORCPT ); Wed, 29 Jul 2015 05:59:25 -0400 Received: from mx2.suse.de ([195.135.220.15]:36340 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750819AbbG2J7X (ORCPT ); Wed, 29 Jul 2015 05:59:23 -0400 Subject: Re: [PATCH 08/10] mm, page_alloc: Remove MIGRATE_RESERVE To: Mel Gorman , Linux-MM References: <1437379219-9160-1-git-send-email-mgorman@suse.com> <1437379219-9160-9-git-send-email-mgorman@suse.com> Cc: Johannes Weiner , Rik van Riel , Pintu Kumar , Xishi Qiu , Gioh Kim , LKML , Mel Gorman From: Vlastimil Babka Message-ID: <55B8A3F3.6090107@suse.cz> Date: Wed, 29 Jul 2015 11:59:15 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.0.1 MIME-Version: 1.0 In-Reply-To: <1437379219-9160-9-git-send-email-mgorman@suse.com> Content-Type: text/plain; charset=iso-8859-2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1433 Lines: 29 On 07/20/2015 10:00 AM, Mel Gorman wrote: > From: Mel Gorman > > MIGRATE_RESERVE preserves an old property of the buddy allocator that existed > prior to fragmentation avoidance -- min_free_kbytes worth of pages tended to > remain free until the only alternative was to fail the allocation. At the ^ I think you meant contiguous instead of free? Is it because splitting chooses lowest possible order, and grouping by mobility means you might be splitting e.g. order-5 movable page instead of using order-0 unmovable page? And that the fallback heuristics specifically select highest available order? I think it's not that obvious, so worth mentioning. > time it was discovered that high-order atomic allocations relied on this > property so MIGRATE_RESERVE was introduced. A later patch will introduce > an alternative MIGRATE_HIGHATOMIC so this patch deletes MIGRATE_RESERVE > and supporting code so it'll be easier to review. Note that this patch > in isolation may look like a false regression if someone was bisecting > high-order atomic allocation failures. > > Signed-off-by: Mel Gorman Acked-by: Vlastimil Babka -- 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/