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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 B7AFEC433DB for ; Wed, 17 Mar 2021 14:51:00 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2F54C64F3E for ; Wed, 17 Mar 2021 14:51:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2F54C64F3E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9DBDE6B007B; Wed, 17 Mar 2021 10:50:59 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 98B6F6B007D; Wed, 17 Mar 2021 10:50:59 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 854866B007E; Wed, 17 Mar 2021 10:50:59 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0036.hostedemail.com [216.40.44.36]) by kanga.kvack.org (Postfix) with ESMTP id 6B2576B007B for ; Wed, 17 Mar 2021 10:50:59 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 288F1180AD822 for ; Wed, 17 Mar 2021 14:50:59 +0000 (UTC) X-FDA: 77929653438.12.A6FFE8E Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf05.hostedemail.com (Postfix) with ESMTP id 9D35DE00307D for ; Wed, 17 Mar 2021 14:38:39 +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 4C4CBAE53; Wed, 17 Mar 2021 14:38:38 +0000 (UTC) Date: Wed, 17 Mar 2021 15:38:35 +0100 From: Oscar Salvador To: Michal Hocko Cc: Andrew Morton , Vlastimil Babka , David Hildenbrand , Muchun Song , Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 2/5] mm,compaction: Let isolate_migratepages_{range,block} return error codes Message-ID: <20210317143827.GA20965@linux> References: <20210317111251.17808-1-osalvador@suse.de> <20210317111251.17808-3-osalvador@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 9D35DE00307D X-Stat-Signature: ynm1n8dnqcpeqqa3g77btqrs4bingfhr Received-SPF: none (suse.de>: No applicable sender policy available) receiver=imf05; identity=mailfrom; envelope-from=""; helo=mx2.suse.de; client-ip=195.135.220.15 X-HE-DKIM-Result: none/none X-HE-Tag: 1615991919-156575 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 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. > > This looks hakish and I cannot really tell that users of cc->migrate_pfn > work as intended. 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 the next pfn to be scanned. But Vlastimil made me realize that since cc->migrate_pfn points to that aleady, so we do not need any extra field. > > @@ -810,6 +811,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > > unsigned long next_skip_pfn = 0; > > bool skip_updated = false; > > > > + cc->migrate_pfn = low_pfn; > > + > > /* > > * Ensure that there are not too many pages isolated from the LRU > > * list by either parallel reclaimers or compaction. If there are, > > @@ -818,16 +821,16 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > > while (unlikely(too_many_isolated(pgdat))) { > > /* stop isolation if there are still pages not migrated */ > > if (cc->nr_migratepages) > > - return 0; > > + return -EINTR; > > > > /* async migration should just abort */ > > if (cc->mode == MIGRATE_ASYNC) > > - return 0; > > + return -EINTR; > > EINTR for anything other than signal based bail out is really confusing. When coding that, I thought about using -1 for the first two checks, and keep -EINTR for the signal check, but isolate_migratepages_block only has two users: - isolate_migratepages: Does not care about the return code other than pfn != 0, and it does not pass the error down the chain. - isolate_migratepages_range: The error is passed down the chain, and !pfn is being treated as -EINTR: static int __alloc_contig_migrate_range(struct compact_control *cc, unsigned long start, unsigned long end) { ... ... pfn = isolate_migratepages_range(cc, pfn, end); if (!pfn) { ret = -EINTR; break; } ... } That is why I decided to stick with -EINTR. -- Oscar Salvador SUSE L3