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=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 32B18C55182 for ; Mon, 20 Apr 2020 22:12:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0F4C120B1F for ; Mon, 20 Apr 2020 22:12:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=cmpxchg-org.20150623.gappssmtp.com header.i=@cmpxchg-org.20150623.gappssmtp.com header.b="jbzqhoEM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728455AbgDTWMS (ORCPT ); Mon, 20 Apr 2020 18:12:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38226 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728430AbgDTWMQ (ORCPT ); Mon, 20 Apr 2020 18:12:16 -0400 Received: from mail-qk1-x741.google.com (mail-qk1-x741.google.com [IPv6:2607:f8b0:4864:20::741]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0A19BC061A0C for ; Mon, 20 Apr 2020 15:12:16 -0700 (PDT) Received: by mail-qk1-x741.google.com with SMTP id g74so12521193qke.13 for ; Mon, 20 Apr 2020 15:12:16 -0700 (PDT) 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:in-reply-to:references :mime-version:content-transfer-encoding; bh=mru2mqYssRMwFvfM60SVK8LHEOtTvwZ9sk9Ozs6ntCE=; b=jbzqhoEM5d7NDzw3vfdtgPSSoDlrWCej+05GdZmq+IawnWaqCKW0HH/bet3KzfXkzI X40GyZbo6g+QTskRmkxQ4BoKE1dowe9171ocp8SAujcL5g1va70+O2r6uieOwu60OKv8 2iBVNUCDBAtCC17cBY5xLP4VqdlKXcG9yz2XzIA5GCVzfi2UTnZy+eQnY/ovTSS3Cfgi LSZ9xrD0VnTnru809Wm7EHvlmTJ7PAPtjZB29vsCjFkd2c0vuv7jfoYdDviMy/qWaLjt yW2FMnGLHwetNA39YeYWTBk6TaxRFtCzGlSWHqLRh9vgdXbHPv8ItR6ybXmvfQgCLRiO 5F6w== 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:in-reply-to :references:mime-version:content-transfer-encoding; bh=mru2mqYssRMwFvfM60SVK8LHEOtTvwZ9sk9Ozs6ntCE=; b=inDFBZZo35MlqqS3J+QIvPQFR9/CQ6bKJP6NXqtZ3L3JWdKZKfOvG5EXtMopE1H0jw PmqS/odralzv2Itphr/RlIdPN5ME+yHHWkUlmrefig6zpWU7U0ptBFlQp8Igs2qFpKUR otD3tA9A1MXgyp+hZx0jBqZXwq+mRF22haJHXTql8gyrwrzvzCpjClG2+arrzqGqyrae zbIb3Mbjj+S3iedaOV4sxqDyRgVmU1lNRumitQClNTxBDr4wRkx1RDc+3RViXRHN7EFM iGnvjNaXYl756aqwQYImNkiUZZcGRf0ZSskVygTYm+P0nFrm555C0M9QpKMEtsUYDCmr yXUA== X-Gm-Message-State: AGi0PubUoqcIXdoNchEv1KSulCOka5pMBP852WAGpiWylYa67scszcc8 bfoPI618K1GxvAlaD9MlZnHJ/w== X-Google-Smtp-Source: APiQypKy4lffy6IiWnR6FoQOXGtMzDxnDrBryWX0kbP1QfAiEJF+n/mTkp0kRiachpRUe+VdcRJLdw== X-Received: by 2002:a37:6587:: with SMTP id z129mr18837123qkb.437.1587420735277; Mon, 20 Apr 2020 15:12:15 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::1:e6b6]) by smtp.gmail.com with ESMTPSA id i56sm521733qte.6.2020.04.20.15.12.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Apr 2020 15:12:14 -0700 (PDT) From: Johannes Weiner To: Joonsoo Kim , Alex Shi Cc: Shakeel Butt , Hugh Dickins , Michal Hocko , "Kirill A. Shutemov" , Roman Gushchin , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: [PATCH 18/18] mm: memcontrol: update page->mem_cgroup stability rules Date: Mon, 20 Apr 2020 18:11:26 -0400 Message-Id: <20200420221126.341272-19-hannes@cmpxchg.org> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200420221126.341272-1-hannes@cmpxchg.org> References: <20200420221126.341272-1-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The previous patches have simplified the access rules around page->mem_cgroup somewhat: 1. We never change page->mem_cgroup while the page is isolated by somebody else. This was by far the biggest exception to our rules and it didn't stop at lock_page() or lock_page_memcg(). 2. We charge pages before they get put into page tables now, so the somewhat fishy rule about "can be in page table as long as it's still locked" is now gone and boiled down to having an exclusive reference to the page. Document the new rules. Any of the following will stabilize the page->mem_cgroup association: - the page lock - LRU isolation - lock_page_memcg() - exclusive access to the page Signed-off-by: Johannes Weiner --- mm/memcontrol.c | 21 +++++++-------------- 1 file changed, 7 insertions(+), 14 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index a8cce52b6b4d..7b63260c9b57 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1201,9 +1201,8 @@ int mem_cgroup_scan_tasks(struct mem_cgroup *memcg, * @page: the page * @pgdat: pgdat of the page * - * This function is only safe when following the LRU page isolation - * and putback protocol: the LRU lock must be held, and the page must - * either be PageLRU() or the caller must have isolated/allocated it. + * This function relies on page->mem_cgroup being stable - see the + * access rules in commit_charge(). */ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgdat) { @@ -2605,18 +2604,12 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg) { VM_BUG_ON_PAGE(page->mem_cgroup, page); /* - * Nobody should be changing or seriously looking at - * page->mem_cgroup at this point: - * - * - the page is uncharged - * - * - the page is off-LRU - * - * - an anonymous fault has exclusive page access, except for - * a locked page table + * Any of the following ensures page->mem_cgroup stability: * - * - a page cache insertion, a swapin fault, or a migration - * have the page locked + * - the page lock + * - LRU isolation + * - lock_page_memcg() + * - exclusive reference */ page->mem_cgroup = memcg; } -- 2.26.0