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Wed, 17 Mar 2021 14:42:46 +0000 (UTC) Received: from [10.36.112.124] (ovpn-112-124.ams2.redhat.com [10.36.112.124]) by smtp.corp.redhat.com (Postfix) with ESMTP id 032255D6AC; Wed, 17 Mar 2021 14:42:44 +0000 (UTC) Subject: Re: [PATCH v5 1/5] mm,page_alloc: Bail out earlier on -ENOMEM in alloc_contig_migrate_range To: Michal Hocko , Oscar Salvador Cc: Andrew Morton , Vlastimil Babka , Muchun Song , Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210317111251.17808-1-osalvador@suse.de> <20210317111251.17808-2-osalvador@suse.de> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <89830f41-b3f2-a158-a173-8c14101edcaa@redhat.com> Date: Wed, 17 Mar 2021 15:42:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Stat-Signature: f7skh4t64tngge7ini9y1iff8rnawnzy X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 35CCFC2CEA69 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf14; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=63.128.21.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615992173-363033 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 17.03.21 15:05, Michal Hocko wrote: > On Wed 17-03-21 12:12:47, Oscar Salvador wrote: >> Currently, __alloc_contig_migrate_range can generate -EINTR, -ENOMEM or -EBUSY, >> and report them down the chain. >> The problem is that when migrate_pages() reports -ENOMEM, we keep going till we >> exhaust all the try-attempts (5 at the moment) instead of bailing out. >> >> migrate_pages() bails out right away on -ENOMEM because it is considered a fatal >> error. Do the same here instead of keep going and retrying. > > I suspect this is not really a real life problem, right? The allocation > would be more costly in the end but this is to be expected under a heavy > memory pressure. > > That being said, bailing out early makes sense to me. But now that > you've made me look into the migrate_pages excellent error state reporting > I suspect we have a bug here. Note the > "Returns the number of pages that were not migrated, or an error code." > > but I do not see putback_movable_pages for ret > 0 so it seems we might > leak some pages. At least in __alloc_contig_migrate_range() we seem to always leave the loop with ret <= 0 and do a putback_movable_pages() with ret < 0. Which code are you referring to? (I think the logic flow inside __alloc_contig_migrate_range() might be improved ...) -- Thanks, David / dhildenb