From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760871Ab3LIIj6 (ORCPT ); Mon, 9 Dec 2013 03:39:58 -0500 Received: from LGEMRELSE1Q.lge.com ([156.147.1.111]:47563 "EHLO LGEMRELSE1Q.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754336Ab3LIIj5 (ORCPT ); Mon, 9 Dec 2013 03:39:57 -0500 X-AuditID: 9c93016f-b7c57ae0000070d3-3e-52a581dbd496 Date: Mon, 9 Dec 2013 17:42:45 +0900 From: Joonsoo Kim To: Naoya Horiguchi Cc: Vlastimil Babka , Andrew Morton , Mel Gorman , Rik van Riel , Rafael Aquini , Christoph Lameter , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 1/4] mm/migrate: correct return value of migrate_pages() Message-ID: <20131209084245.GA27201@lge.com> References: <1386319310-28016-1-git-send-email-iamjoonsoo.kim@lge.com> <52A1E248.1000204@suse.cz> <1386355046-jja39cg0-mutt-n-horiguchi@ah.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1386355046-jja39cg0-mutt-n-horiguchi@ah.jp.nec.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 06, 2013 at 01:37:26PM -0500, Naoya Horiguchi wrote: > On Fri, Dec 06, 2013 at 03:42:16PM +0100, Vlastimil Babka wrote: > > On 12/06/2013 09:41 AM, Joonsoo Kim wrote: > > >migrate_pages() should return number of pages not migrated or error code. > > >When unmap_and_move return -EAGAIN, outer loop is re-execution without > > >initialising nr_failed. This makes nr_failed over-counted. > > > > > >So this patch correct it by initialising nr_failed in outer loop. > > > > > >Signed-off-by: Joonsoo Kim > > > > > >diff --git a/mm/migrate.c b/mm/migrate.c > > >index 3747fcd..1f59ccc 100644 > > >--- a/mm/migrate.c > > >+++ b/mm/migrate.c > > >@@ -1102,6 +1102,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, > > > > > > for(pass = 0; pass < 10 && retry; pass++) { > > > retry = 0; > > >+ nr_failed = 0; > > > > > > list_for_each_entry_safe(page, page2, from, lru) { > > > cond_resched(); > > > > > > > If I'm reading the code correctly, unmap_and_move() (and > > unmap_and_move_huge_page() as well) deletes all pages from the > > 'from' list, unless it fails with -EAGAIN. So the only pages you see > > in subsequent passes are those that failed with -EAGAIN and those > > are not counted as nr_failed. So there shouldn't be over-count, but > > your patch could result in under-count. > > > > Perhaps a comment somewhere would clarify this. > > I agree and suggest the one below. > Joonsoo, feel free to append it to your series:) > > Thanks, > Naoya Horiguchi > --- > From: Naoya Horiguchi > Date: Fri, 6 Dec 2013 13:08:15 -0500 > Subject: [PATCH] migrate: add comment about permanent failure path > > Let's add a comment about where the failed page goes to, which makes > code more readable. > > Signed-off-by: Naoya Horiguchi > --- > mm/migrate.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 661ff5f66591..c01caafa0a6f 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1118,7 +1118,12 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, > nr_succeeded++; > break; > default: > - /* Permanent failure */ > + /* > + * Permanent failure (-EBUSY, -ENOSYS, etc.): > + * unlike -EAGAIN case, the failed page is > + * removed from migration page list and not > + * retried in the next outer loop. > + */ > nr_failed++; > break; > } > -- > 1.8.3.1 Hello, Naoya. When I saw this new comment, I found that unmap_and_move_huge_page() has a bug. It would not remove the page from the list if hugepage_migration_support() is false. I will include your patch into my series and send an additional patch to fix this problem. Thanks.