Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752965AbaBJN0j (ORCPT ); Mon, 10 Feb 2014 08:26:39 -0500 Received: from cantor2.suse.de ([195.135.220.15]:48429 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752195AbaBJN0i (ORCPT ); Mon, 10 Feb 2014 08:26:38 -0500 Date: Mon, 10 Feb 2014 13:26:34 +0000 From: Mel Gorman To: Joonsoo Kim Cc: Andrew Morton , Vlastimil Babka , Joonsoo Kim , Rik van Riel , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/5] mm/compaction: disallow high-order page for migration target Message-ID: <20140210132634.GE6732@suse.de> References: <1391749726-28910-1-git-send-email-iamjoonsoo.kim@lge.com> <1391749726-28910-2-git-send-email-iamjoonsoo.kim@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1391749726-28910-2-git-send-email-iamjoonsoo.kim@lge.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 07, 2014 at 02:08:42PM +0900, Joonsoo Kim wrote: > Purpose of compaction is to get a high order page. Currently, if we find > high-order page while searching migration target page, we break it to > order-0 pages and use them as migration target. It is contrary to purpose > of compaction, so disallow high-order page to be used for > migration target. > > Additionally, clean-up logic in suitable_migration_target() to simply. > There is no functional changes from this clean-up. > > Signed-off-by: Joonsoo Kim > > diff --git a/mm/compaction.c b/mm/compaction.c > index 3a91a2e..bbe1260 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -217,21 +217,12 @@ static inline bool compact_trylock_irqsave(spinlock_t *lock, > /* Returns true if the page is within a block suitable for migration to */ > static bool suitable_migration_target(struct page *page) > { > - int migratetype = get_pageblock_migratetype(page); > - > - /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */ > - if (migratetype == MIGRATE_RESERVE) > - return false; > - Why is this check removed? The reservation blocks are preserved as short-lived high-order atomic allocations depend on them. > - if (is_migrate_isolate(migratetype)) > - return false; > - Why is this check removed? > - /* If the page is a large free page, then allow migration */ > + /* If the page is a large free page, then disallow migration */ > if (PageBuddy(page) && page_order(page) >= pageblock_order) > - return true; > + return false; > The reason why this was originally allowed was to allow pageblocks that were marked MIGRATE_UNMOVABLE or MIGRATE_RECLAIMABLE to be used as compaction targets. However, compaction should not even be running if this is the case so the change makes sense. > /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */ > - if (migrate_async_suitable(migratetype)) > + if (migrate_async_suitable(get_pageblock_migratetype(page))) > return true; > > /* Otherwise skip the block */ > -- > 1.7.9.5 > -- Mel Gorman SUSE Labs -- 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/