From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx186.postini.com [74.125.245.186]) by kanga.kvack.org (Postfix) with SMTP id 3A5DF6B00A1 for ; Tue, 3 Jul 2012 17:48:10 -0400 (EDT) Date: Tue, 3 Jul 2012 14:48:08 -0700 From: Andrew Morton Subject: Re: [PATCH -mm v2] mm: have order > 0 compaction start off where it left Message-Id: <20120703144808.4daa4244.akpm@linux-foundation.org> In-Reply-To: <20120703101024.GG13141@csn.ul.ie> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Rik van Riel , Sasha Levin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, jaschut@sandia.gov, minchan@kernel.org, kamezawa.hiroyu@jp.fujitsu.com, Dave Jones 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? -- 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