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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 15A8BC433E0 for ; Mon, 1 Feb 2021 06:07:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5BCEC64E2F for ; Mon, 1 Feb 2021 06:07:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5BCEC64E2F 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 A84A16B0006; Mon, 1 Feb 2021 01:07:05 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A35896B006C; Mon, 1 Feb 2021 01:07:05 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 94C4A6B006E; Mon, 1 Feb 2021 01:07:05 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0118.hostedemail.com [216.40.44.118]) by kanga.kvack.org (Postfix) with ESMTP id 7C9926B0006 for ; Mon, 1 Feb 2021 01:07:05 -0500 (EST) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 486C83631 for ; Mon, 1 Feb 2021 06:07:05 +0000 (UTC) X-FDA: 77768666010.09.teeth53_5611593275bf Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin09.hostedemail.com (Postfix) with ESMTP id 2AEA3180AD81A for ; Mon, 1 Feb 2021 06:07:05 +0000 (UTC) X-HE-Tag: teeth53_5611593275bf X-Filterd-Recvd-Size: 2683 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Mon, 1 Feb 2021 06:07:04 +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 48432B125; Mon, 1 Feb 2021 06:07:03 +0000 (UTC) From: Oscar Salvador To: akpm@linux-foundation.org Cc: hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oscar Salvador Subject: [PATCH] mm: workingset: clarify eviction order and distance calculation Date: Mon, 1 Feb 2021 07:06:51 +0100 Message-Id: <20210201060651.3781-1-osalvador@suse.de> X-Mailer: git-send-email 2.28.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000038, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The premise of the refault distance is that it can be seen as a deficit of the inactive list space, so that if the inactive list would have had (R - E) more slots, the page would not have been evicted but promoted to the active list instead. However, the way the code is ordered right now set us to be off by one, so the real number of slots would be (R - E) + 1. I stumbled upon this when trying to understand the code and it puzzled me that the comments did not match what the code did. This it not an issue at all since evictions and refaults tend to happen in a number large enough that being off-by-one does not have any impact - and since the compiler and CPUs are free to rearrange the execution sequence anyway. But as Johannes says, it is better to re-arrange the code in the proper order since otherwise would be misleading to somebody who is actively reading and trying to understand the logic of the code - like it happened to me. Signed-off-by: Oscar Salvador Acked-by: Johannes Weiner --- mm/workingset.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/workingset.c b/mm/workingset.c index 10e96de945b3..0201aa1ff320 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -263,10 +263,10 @@ void *workingset_eviction(struct page *page, struct= mem_cgroup *target_memcg) VM_BUG_ON_PAGE(!PageLocked(page), page); =20 lruvec =3D mem_cgroup_lruvec(target_memcg, pgdat); - workingset_age_nonresident(lruvec, thp_nr_pages(page)); /* XXX: target_memcg can be NULL, go through lruvec */ memcgid =3D mem_cgroup_id(lruvec_memcg(lruvec)); eviction =3D atomic_long_read(&lruvec->nonresident_age); + workingset_age_nonresident(lruvec, thp_nr_pages(page)); return pack_shadow(memcgid, pgdat, eviction, PageWorkingset(page)); } =20 --=20 2.26.2