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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id A7B40C48BC4 for ; Tue, 20 Feb 2024 04:10:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 312416B006E; Mon, 19 Feb 2024 23:10:08 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2C2366B007E; Mon, 19 Feb 2024 23:10:08 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 189936B0082; Mon, 19 Feb 2024 23:10:08 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 041466B007E for ; Mon, 19 Feb 2024 23:10:08 -0500 (EST) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id C21C2C0576 for ; 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imf12.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf12.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1708402206; a=rsa-sha256; cv=none; b=NShj1Evl6j+FI3TLgq+itC91u2IDyEhxn/ooAoftCv8a+coOFLbiqagwyi8d8kOe+Eojkg bUXpwEe2Fnzxb7+V35U0qOhmnVJjPC4cFKQ4QzxUXp/hmfCN7aBXvd2w89IgVUPRiHhP4X 2xK06fUIucudarAZRyveVVjA7b+jacs= X-AuditID: a67dfc5b-d85ff70000001748-e6-65d4261705ab Date: Tue, 20 Feb 2024 13:09:54 +0900 From: Byungchul Park To: Andrew Morton Cc: "Huang, Ying" , mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com Subject: Re: [PATCH v4] sched/numa, mm: do not try to migrate memory to memoryless nodes Message-ID: <20240220040954.GJ65758@system.software.com> References: <20240219041920.1183-1-byungchul@sk.com> <87o7ccrghz.fsf@yhuang6-desk2.ccr.corp.intel.com> <20240219174508.bc6256248a163c3ab9a58369@linux-foundation.org> <20240220023304.GF65758@system.software.com> <20240219192841.f1ed44b8c85073511227721c@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; 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I posted the following > > two patches while resolving the oops issue. However, two are going on > > for different purposes. > > > > 1) https://lkml.kernel.org/r/20240219041920.1183-1-byungchul@sk.com > > > > I started this patch as the fix for the oops. However, I found the > > root cause comes from using -1 as an array index. So let the root > > cause fix go with another thread, 2). Nevertheless, 1) is still > > necessary as a *reasonable optimization* but not the real fix any > > more. > > Well I altered this patch's changelog to tell readers that it is an > optimization. But one does wonder why it isn't simply a bugfix. > Attempting to migrate to a memoryless node is clearly as error. I agree with what Oscar Salvador said: "As this is not a bug fix but an optimization, as we will fail anyways in migrate_misplaced_folio() when migrate_balanced_pgdat() notices that we do not have any memory on that node." https://lore.kernel.org/lkml/ZdG1yO29WTyRiw8Q@localhost.localdomain/ So assuming all the related code works correctly, the migration will safely fail even without this optimization patch. Byungchul > Presumably the called code handles it somehow, but in what fashion and > at what cost? > > > 2) https://lkml.kernel.org/r/20240216111502.79759-1-byungchul@sk.com > > > > I found the root cause of the oops comes from using -1 as an array > > index. So moved all the oops message, Fixes: tag, and cc stable to > > here. Long story short, 2) is the *real fix* for the oops. > >