From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A3C0C433DB for ; Thu, 18 Mar 2021 09:50:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A9FDA64F30 for ; Thu, 18 Mar 2021 09:50:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A9FDA64F30 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2DE9D6B0070; Thu, 18 Mar 2021 05:50:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 28E096B0071; Thu, 18 Mar 2021 05:50:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 12F4B6B0072; Thu, 18 Mar 2021 05:50:41 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0041.hostedemail.com [216.40.44.41]) by kanga.kvack.org (Postfix) with ESMTP id E7AB66B0070 for ; Thu, 18 Mar 2021 05:50:40 -0400 (EDT) Received: from smtpin39.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id B0AB212DC for ; Thu, 18 Mar 2021 09:50:40 +0000 (UTC) X-FDA: 77932525440.39.4A3C071 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf21.hostedemail.com (Postfix) with ESMTP id 24117E0001B2 for ; Thu, 18 Mar 2021 09:50:40 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id D2AA5AD4A; Thu, 18 Mar 2021 09:50:38 +0000 (UTC) To: Michal Hocko , Oscar Salvador Cc: Andrew Morton , David Hildenbrand , Muchun Song , Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210317111251.17808-1-osalvador@suse.de> <20210317111251.17808-3-osalvador@suse.de> <20210317143827.GA20965@linux> From: Vlastimil Babka Subject: Re: [PATCH v5 2/5] mm,compaction: Let isolate_migratepages_{range,block} return error codes Message-ID: <843f68e7-6fe6-54e7-976b-af8647482ac1@suse.cz> Date: Thu, 18 Mar 2021 10:50:38 +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 Content-Language: en-US X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 24117E0001B2 X-Stat-Signature: sjkb3q6rfd4phqddd7zsm1pnba9iwpkt Received-SPF: none (suse.cz>: No applicable sender policy available) receiver=imf21; identity=mailfrom; envelope-from=""; helo=mx2.suse.de; client-ip=195.135.220.15 X-HE-DKIM-Result: none/none X-HE-Tag: 1616061040-298348 Content-Transfer-Encoding: quoted-printable 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 3/17/21 3:59 PM, Michal Hocko wrote: > On Wed 17-03-21 15:38:35, Oscar Salvador wrote: >> On Wed, Mar 17, 2021 at 03:12:29PM +0100, Michal Hocko wrote: >> > > Since isolate_migratepages_block will stop returning the next pfn = to be >> > > scanned, we reuse the cc->migrate_pfn field to keep track of that. >> >=20 >> > This looks hakish and I cannot really tell that users of cc->migrate= _pfn >> > work as intended. We did check those in detail. Of course it's possible to overlook somethi= ng... The alloc_contig_range user never cared about cc->migrate_pfn. compaction (isolate_migratepages() -> isolate_migratepages_block()) did, and isolate_migratepages_block() returned the pfn only to be assigned to cc->migrate_pfn in isolate_migratepages(). I think it's now better that isolate_migratepages_block() sets it. >> When discussing this with Vlastimil, I came up with the idea of adding= a new >> field in compact_control struct, e.g: next_pfn_scan to keep track of t= he next >> pfn to be scanned. >>=20 >> But Vlastimil made me realize that since cc->migrate_pfn points to tha= t aleady, >> so we do not need any extra field. Yes, the first patch had at asome point: /* Record where migration scanner will be restarted. */ cc->migrate_pfn =3D cc->the_new_field; Which was a clear sign that the new field is unnecessary. > This deserves a big fat comment. Comment where, saying what? :)