From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx108.postini.com [74.125.245.108]) by kanga.kvack.org (Postfix) with SMTP id 1B2DB6B0078 for ; Tue, 3 Jul 2012 22:33:30 -0400 (EDT) Message-ID: <4FF3ABA1.3070808@kernel.org> Date: Wed, 04 Jul 2012 11:34:09 +0900 From: Minchan Kim MIME-Version: 1.0 Subject: Re: [PATCH -mm v2] mm: have order > 0 compaction start off where it left References: <20120628135520.0c48b066@annuminas.surriel.com> <20120628135940.2c26ada9.akpm@linux-foundation.org> <4FECCB89.2050400@redhat.com> <20120628143546.d02d13f9.akpm@linux-foundation.org> <1341250950.16969.6.camel@lappy> <4FF2435F.2070302@redhat.com> <20120703101024.GG13141@csn.ul.ie> <20120703144808.4daa4244.akpm@linux-foundation.org> In-Reply-To: <20120703144808.4daa4244.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Mel Gorman , Rik van Riel , Sasha Levin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, jaschut@sandia.gov, kamezawa.hiroyu@jp.fujitsu.com, Dave Jones Hi Andrew, On 07/04/2012 06:48 AM, Andrew Morton wrote: > On Tue, 3 Jul 2012 11:10:24 +0100 > Mel Gorman wrote: > >>>>>>>> + if (cc->order> 0) >>>>>>>> + zone->compact_cached_free_pfn = high_pfn; >>>>>>> >>>>>>> Is high_pfn guaranteed to be aligned to pageblock_nr_pages here? I >>>>>>> assume so, if lots of code in other places is correct but it's >>>>>>> unobvious from reading this function. >>>>>> >>>>>> Reading the code a few more times, I believe that it is >>>>>> indeed aligned to pageblock size. >>>>> >>>>> I'll slip this into -next for a while. >>>>> >>>>> --- a/mm/compaction.c~isolate_freepages-check-that-high_pfn-is-aligned-as-expected >>>>> +++ a/mm/compaction.c >>>>> @@ -456,6 +456,7 @@ static void isolate_freepages(struct zon >>>>> } >>>>> spin_unlock_irqrestore(&zone->lock, flags); >>>>> >>>>> + WARN_ON_ONCE(high_pfn& (pageblock_nr_pages - 1)); >>>>> /* >>>>> * Record the highest PFN we isolated pages from. When next >>>>> * looking for free pages, the search will restart here as >>>> >>>> I've triggered the following with today's -next: >>> >>> I've been staring at the migrate code for most of the afternoon, >>> and am not sure how this is triggered. >>> >> >> That warning is placed in isolate_freepages(). When the migration >> scanner and free scanner have almost met it is possible for high_pfn to >> be >> >> cc->migrate_pfn + pageblock_nr_pages >> >> and that is not necessarily pageblock aligned. Forcing it to be aligned >> raises the possibility that the free scanner moves to another zone. This >> is very unlikely but could happen if a high zone was very small. >> >> I should have caught this when the warning was proposed :( IMO it's >> safe to just drop the warning. > > The rest of this patch takes care to ensure that > ->compact_cached_free_pfn is aligned to pageblock_nr_pages. But it now > appears that this particular site will violate that. > > What's up? Do we need to fix this site, or do we remove all that > make-compact_cached_free_pfn-aligned code? I vote removing the warning because it doesn't related to Rik's incremental compaction. Let's see. high_pfn = min(low_pfn, pfn) = cc->migrate_pfn + pageblock_nr_pages. In here, cc->migrate_pfn isn't necessarily pageblock aligined. So if we don't consider compact_cached_free_pfn, it can hit. static void isolate_freepages() { high_pfn = min(low_pfn, pfn) = cc->migrate_pfn + pageblock_nr_pages; for (..) { ... WARN_ON_ONCE(high_pfn & (pageblock_nr_pages - 1)); } } -- Kind regards, Minchan Kim -- 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