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=-16.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 7A04FC433E6 for ; Tue, 2 Feb 2021 18:44:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id ED23D64F4B for ; Tue, 2 Feb 2021 18:44:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org ED23D64F4B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=cmpxchg.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 7D53A6B0005; Tue, 2 Feb 2021 13:44:14 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 784A06B006C; Tue, 2 Feb 2021 13:44:14 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6C4DB6B0070; Tue, 2 Feb 2021 13:44:14 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0215.hostedemail.com [216.40.44.215]) by kanga.kvack.org (Postfix) with ESMTP id 576F86B0005 for ; Tue, 2 Feb 2021 13:44:14 -0500 (EST) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 1E3F28249980 for ; Tue, 2 Feb 2021 18:44:14 +0000 (UTC) X-FDA: 77774202828.04.quiet66_31150e8275cd Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin04.hostedemail.com (Postfix) with ESMTP id F242F800CF12 for ; Tue, 2 Feb 2021 18:44:13 +0000 (UTC) X-HE-Tag: quiet66_31150e8275cd X-Filterd-Recvd-Size: 5163 Received: from mail-qk1-f177.google.com (mail-qk1-f177.google.com [209.85.222.177]) by imf09.hostedemail.com (Postfix) with ESMTP for ; Tue, 2 Feb 2021 18:44:13 +0000 (UTC) Received: by mail-qk1-f177.google.com with SMTP id n15so20847387qkh.8 for ; Tue, 02 Feb 2021 10:44:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=6NrYwMryjhSf8mb6qdDWT1m6IwDhTR3/t7R1WlKEKoI=; b=WLd+qHBVqRdD250/aYzj9n/ag1cWfmEHEDwFhQuNz21u2ptdc+L+vQl/LLxjhNbKsI ES7/wJd2DxX8IWjGzN1+xNuiZJCyjaxsf2EKFhyKUl8sxBMPFRfG7RHt1f6TKWp+X9Vk 3gqkNpPBGMfsUkXJKwDBYmpSqdBgvf0DyZuCAZ8+S4mxms04TX6L4UoSHKbexEkgyFNP Ckx8Ybq64XG82JKWmeLCZHNQ5MkRkmmtc5WOkPoZ4LbowWPlTfhgk7RtsahV75rxyhi9 7P+fV3nHLPSChNwTskvKY/bFGwbM3vjFQVEk4lA/LzoZhRW/jAbJKyvxKUAsmTupqEb7 jhgg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=6NrYwMryjhSf8mb6qdDWT1m6IwDhTR3/t7R1WlKEKoI=; b=WzQMUnL6/UZ3HUm5yTrF3ribf50o56xsRMiirBEnguntJYgORLtSZTfKFMu8s2aIOz +0oXXK96taG/b7bwJUJZHfxwTyZs2/xu3gnzlod1tNA+4N9THMj7/rISGhEtZg5jjcRW FOlY+i81T3HWIZBV1v2aZ8Ta3MshI/Oeh4w+prD63VIFRp0gc1NUCXloWH8j0PI5dGKf GInxZj84Gdp1JtQP5YeqY2SBjciu40UykCGMn97RrcFrdFFbsJ0hfXjt8m+Ue4rqxC7L 9g8V3Pd0MODk365XaJxik6AWxXC/Wp3QuxmBqNSPZbL6EB+7bgcZjMKXNvFFtOgxPrFV O2vA== X-Gm-Message-State: AOAM530o5ma3bn9trBnbY6t33/Hfk5LKpmgtk5FvnPPdK8lDc0zPfJ8B cas4EXHZbdN7nzdBtKxU/E9WBA== X-Google-Smtp-Source: ABdhPJwExZvBVVEUtLaD1ZuRfZiAGXecrwPpVpHunS7NXDpk+oqMsb7jUQEKW7IIQU99XQGapTqPqg== X-Received: by 2002:a37:4d8e:: with SMTP id a136mr21354060qkb.317.1612291452536; Tue, 02 Feb 2021 10:44:12 -0800 (PST) Received: from localhost (70.44.39.90.res-cmts.bus.ptd.net. [70.44.39.90]) by smtp.gmail.com with ESMTPSA id x74sm16903842qkb.55.2021.02.02.10.44.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Feb 2021 10:44:11 -0800 (PST) From: Johannes Weiner To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: [PATCH] mm: vmstat: add some comments on internal storage of byte items Date: Tue, 2 Feb 2021 13:44:11 -0500 Message-Id: <20210202184411.118614-1-hannes@cmpxchg.org> X-Mailer: git-send-email 2.30.0 MIME-Version: 1.0 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: Byte-accounted items are used for slab object accounting at the cgroup level, because the objects in a slab page can belong to different cgroups. At the global level these items always change in multiples of whole slab pages. The vmstat code exploits this and stores these items as pages internally, which allows for more compact per-cpu data. This optimization isn't self-evident from the asserts and the division in the stat update functions. Provide the reader with some context. Signed-off-by: Johannes Weiner --- include/linux/vmstat.h | 6 ++++++ mm/vmstat.c | 12 ++++++++++++ 2 files changed, 18 insertions(+) diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h index 773135fc6e19..506d625163a1 100644 --- a/include/linux/vmstat.h +++ b/include/linux/vmstat.h @@ -313,6 +313,12 @@ static inline void __mod_node_page_state(struct pgli= st_data *pgdat, enum node_stat_item item, int delta) { if (vmstat_item_in_bytes(item)) { + /* + * Only cgroups use subpage accounting right now; at + * the global level, these items still change in + * multiples of whole pages. Store them as pages + * internally to keep the per-cpu counters compact. + */ VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1)); delta >>=3D PAGE_SHIFT; } diff --git a/mm/vmstat.c b/mm/vmstat.c index 1cf549dd703e..eff67397301b 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -346,6 +346,12 @@ void __mod_node_page_state(struct pglist_data *pgdat= , enum node_stat_item item, long t; =20 if (vmstat_item_in_bytes(item)) { + /* + * Only cgroups use subpage accounting right now; at + * the global level, these items still change in + * multiples of whole pages. Store them as pages + * internally to keep the per-cpu counters compact. + */ VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1)); delta >>=3D PAGE_SHIFT; } @@ -555,6 +561,12 @@ static inline void mod_node_state(struct pglist_data= *pgdat, long o, n, t, z; =20 if (vmstat_item_in_bytes(item)) { + /* + * Only cgroups use subpage accounting right now; at + * the global level, these items still change in + * multiples of whole pages. Store them as pages + * internally to keep the per-cpu counters compact. + */ VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1)); delta >>=3D PAGE_SHIFT; } --=20 2.30.0