From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755940AbcETNTQ (ORCPT ); Fri, 20 May 2016 09:19:16 -0400 Received: from mx2.suse.de ([195.135.220.15]:35641 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755207AbcETNTP (ORCPT ); Fri, 20 May 2016 09:19:15 -0400 Subject: Re: [patch] mm, migrate: increment fail count on ENOMEM To: Michal Hocko , David Rientjes References: <20160520130649.GB5197@dhcp22.suse.cz> Cc: Andrew Morton , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org From: Vlastimil Babka Message-ID: <573F0ED0.4010908@suse.cz> Date: Fri, 20 May 2016 15:19:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2 MIME-Version: 1.0 In-Reply-To: <20160520130649.GB5197@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/20/2016 03:06 PM, Michal Hocko wrote: > On Thu 19-05-16 15:11:23, David Rientjes wrote: >> If page migration fails due to -ENOMEM, nr_failed should still be >> incremented for proper statistics. >> >> This was encountered recently when all page migration vmstats showed 0, >> and inferred that migrate_pages() was never called, although in reality >> the first page migration failed because compaction_alloc() failed to find >> a migration target. >> >> This patch increments nr_failed so the vmstat is properly accounted on >> ENOMEM. >> >> Signed-off-by: David Rientjes > > Acked-by: Michal Hocko Acked-by: Vlastimil Babka > One question though > >> --- >> mm/migrate.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1171,6 +1171,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, >> >> switch(rc) { >> case -ENOMEM: >> + nr_failed++; >> goto out; >> case -EAGAIN: >> retry++; > > Why don't we need also to count also retries? We could, but not like you suggest. > --- > diff --git a/mm/migrate.c b/mm/migrate.c > index 53ab6398e7a2..ef9c5211ae3c 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1190,9 +1190,9 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, > } > } > } > +out: > nr_failed += retry; > rc = nr_failed; This overwrites rc == -ENOMEM, which at least compaction needs to recognize. But we could duplicate "nr_failed += retry" in the case -ENOMEM. > -out: > if (nr_succeeded) > count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded); > if (nr_failed) >