From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f174.google.com (mail-wi0-f174.google.com [209.85.212.174]) by kanga.kvack.org (Postfix) with ESMTP id 9F1656B007B for ; Fri, 12 Jun 2015 05:55:34 -0400 (EDT) Received: by wibut5 with SMTP id ut5so13354507wib.1 for ; Fri, 12 Jun 2015 02:55:34 -0700 (PDT) Received: from mail-wi0-x236.google.com (mail-wi0-x236.google.com. [2a00:1450:400c:c05::236]) by mx.google.com with ESMTPS id gh11si6247511wjc.11.2015.06.12.02.55.32 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 12 Jun 2015 02:55:33 -0700 (PDT) Received: by wiwd19 with SMTP id d19so13388181wiw.0 for ; Fri, 12 Jun 2015 02:55:32 -0700 (PDT) From: Michal Nazarewicz Subject: Re: [PATCH 1/6] mm, compaction: more robust check for scanners meeting In-Reply-To: <1433928754-966-2-git-send-email-vbabka@suse.cz> References: <1433928754-966-1-git-send-email-vbabka@suse.cz> <1433928754-966-2-git-send-email-vbabka@suse.cz> Date: Fri, 12 Jun 2015 11:55:29 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka , Andrew Morton , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Minchan Kim , Mel Gorman , Joonsoo Kim , Naoya Horiguchi , Christoph Lameter , Rik van Riel , David Rientjes On Wed, Jun 10 2015, Vlastimil Babka wrote: > Compaction should finish when the migration and free scanner meet, i.e. t= hey > reach the same pageblock. Currently however, the test in compact_finished= () > simply just compares the exact pfns, which may yield a false negative whe= n the > free scanner position is in the middle of a pageblock and the migration s= canner > reaches the beginning of the same pageblock. > > This hasn't been a problem until commit e14c720efdd7 ("mm, compaction: re= member > position within pageblock in free pages scanner") allowed the free scanner > position to be in the middle of a pageblock between invocations. The hot= -fix > 1d5bfe1ffb5b ("mm, compaction: prevent infinite loop in compact_zone") > prevented the issue by adding a special check in the migration scanner to > satisfy the current detection of scanners meeting. > > However, the proper fix is to make the detection more robust. This patch > introduces the compact_scanners_met() function that returns true when the= free > scanner position is in the same or lower pageblock than the migration sca= nner. > The special case in isolate_migratepages() introduced by 1d5bfe1ffb5b is > removed. > > Suggested-by: Joonsoo Kim > Signed-off-by: Vlastimil Babka > Cc: Minchan Kim > Cc: Mel Gorman > Cc: Joonsoo Kim > Cc: Michal Nazarewicz Acked-by: Michal Nazarewicz > Cc: Naoya Horiguchi > Cc: Christoph Lameter > Cc: Rik van Riel > Cc: David Rientjes > --- > mm/compaction.c | 22 ++++++++++++++-------- > 1 file changed, 14 insertions(+), 8 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 16e1b57..d46aaeb 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -902,6 +902,16 @@ static bool suitable_migration_target(struct page *p= age) > } >=20=20 > /* > + * Test whether the free scanner has reached the same or lower pageblock= than > + * the migration scanner, and compaction should thus terminate. > + */ > +static inline bool compact_scanners_met(struct compact_control *cc) > +{ > + return (cc->free_pfn >> pageblock_order) > + <=3D (cc->migrate_pfn >> pageblock_order); > +} > + > +/* > * Based on information in the current compact_control, find blocks > * suitable for isolating free pages from and then isolate them. > */ > @@ -1131,12 +1141,8 @@ static isolate_migrate_t isolate_migratepages(stru= ct zone *zone, > } >=20=20 > acct_isolated(zone, cc); > - /* > - * Record where migration scanner will be restarted. If we end up in > - * the same pageblock as the free scanner, make the scanners fully > - * meet so that compact_finished() terminates compaction. > - */ > - cc->migrate_pfn =3D (end_pfn <=3D cc->free_pfn) ? low_pfn : cc->free_pf= n; > + /* Record where migration scanner will be restarted. */ > + cc->migrate_pfn =3D low_pfn; >=20=20 > return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE; > } > @@ -1151,7 +1157,7 @@ static int __compact_finished(struct zone *zone, st= ruct compact_control *cc, > return COMPACT_PARTIAL; >=20=20 > /* Compaction run completes if the migrate and free scanner meet */ > - if (cc->free_pfn <=3D cc->migrate_pfn) { > + if (compact_scanners_met(cc)) { > /* Let the next compaction start anew. */ > zone->compact_cached_migrate_pfn[0] =3D zone->zone_start_pfn; > zone->compact_cached_migrate_pfn[1] =3D zone->zone_start_pfn; > @@ -1380,7 +1386,7 @@ static int compact_zone(struct zone *zone, struct c= ompact_control *cc) > * migrate_pages() may return -ENOMEM when scanners meet > * and we want compact_finished() to detect it > */ > - if (err =3D=3D -ENOMEM && cc->free_pfn > cc->migrate_pfn) { > + if (err =3D=3D -ENOMEM && !compact_scanners_met(cc)) { > ret =3D COMPACT_PARTIAL; > goto out; > } > --=20 > 2.1.4 > --=20 Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=3D./ `o ..o | Computer Science, Micha=C5=82 =E2=80=9Cmina86=E2=80=9D Nazarewicz = (o o) ooo +------ooO--(_)--Ooo-- -- 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