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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 8A80EC4361B for ; Tue, 15 Dec 2020 22:21:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5DFF222D07 for ; Tue, 15 Dec 2020 22:21:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729857AbgLOWVX (ORCPT ); Tue, 15 Dec 2020 17:21:23 -0500 Received: from mail.kernel.org ([198.145.29.99]:45020 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728174AbgLOWVU (ORCPT ); Tue, 15 Dec 2020 17:21:20 -0500 Date: Tue, 15 Dec 2020 14:20:37 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1608070839; bh=PMreW2R4Vi4QzUU4z1kWWF1Hlk7nQ75NLwcVJaoR06g=; h=From:To:Subject:In-Reply-To:From; b=YV9b+0BfadFekoEFh2WCEQ3s7Xj3jtVJ74aJl0mmpmgTrnTZDOIgd8EwyLMRGnNk+ 6vOKqzoWkw10Fx1alUcqJNglvrr3lnJ5pz4qVIjJB7txWEQwHL+xfd5ekzdO+0EMvX Y0WR0hBQ42d3zKNxPv4i63ZBhIq/uPmRQeuWJIdg= From: Andrew Morton To: aarcange@redhat.com, akpm@linux-foundation.org, alex.shi@linux.alibaba.com, alexander.duyck@gmail.com, aryabinin@virtuozzo.com, daniel.m.jordan@oracle.com, hannes@cmpxchg.org, hughd@google.com, iamjoonsoo.kim@lge.com, jannh@google.com, khlebnikov@yandex-team.ru, kirill.shutemov@linux.intel.com, kirill@shutemov.name, linux-mm@kvack.org, mgorman@techsingularity.net, mhocko@kernel.org, mhocko@suse.com, mika.penttila@nextfour.com, minchan@kernel.org, mm-commits@vger.kernel.org, richard.weiyang@gmail.com, rong.a.chen@intel.com, shakeelb@google.com, tglx@linutronix.de, tj@kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz, vdavydov.dev@gmail.com, willy@infradead.org, yang.shi@linux.alibaba.com, ying.huang@intel.com Subject: [patch 07/19] mm: page_idle_get_page() does not need lru_lock Message-ID: <20201215222037.YKqq5CCoZ%akpm@linux-foundation.org> In-Reply-To: <20201215123253.954eca9a5ef4c0d52fd381fa@linux-foundation.org> User-Agent: s-nail v14.8.16 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org =46rom: Hugh Dickins Subject: mm: page_idle_get_page() does not need lru_lock It is necessary for page_idle_get_page() to recheck PageLRU() after get_page_unless_zero(), but holding lru_lock around that serves no useful purpose, and adds to lru_lock contention: delete it. See https://lore.kernel.org/lkml/20150504031722.GA2768@blaptop for the discussion that led to lru_lock there; but __page_set_anon_rmap() now uses WRITE_ONCE(), and I see no other risk in page_idle_clear_pte_refs() using rmap_walk() (beyond the risk of racing PageAnon->PageKsm, mostly but not entirely prevented by page_count() check in ksm.c's write_protect_page(): that risk being shared with page_referenced() and not helped by lru_lock). Link: https://lkml.kernel.org/r/1604566549-62481-8-git-send-email-alex.shi@= linux.alibaba.com Signed-off-by: Hugh Dickins Signed-off-by: Alex Shi Acked-by: Johannes Weiner Acked-by: "Huang, Ying" Acked-by: Vlastimil Babka Cc: Vladimir Davydov Cc: Minchan Kim Cc: Alex Shi Cc: Alexander Duyck Cc: Andrea Arcangeli Cc: Andrey Ryabinin Cc: "Chen, Rong A" Cc: Daniel Jordan Cc: Jann Horn Cc: Joonsoo Kim Cc: Kirill A. Shutemov Cc: Kirill A. Shutemov Cc: Konstantin Khlebnikov Cc: Matthew Wilcox (Oracle) Cc: Mel Gorman Cc: Michal Hocko Cc: Michal Hocko Cc: Mika Penttil=C3=A4 Cc: Shakeel Butt Cc: Tejun Heo Cc: Thomas Gleixner Cc: Wei Yang Cc: Yang Shi Signed-off-by: Andrew Morton --- mm/page_idle.c | 4 ---- 1 file changed, 4 deletions(-) --- a/mm/page_idle.c~mm-page_idle_get_page-does-not-need-lru_lock +++ a/mm/page_idle.c @@ -32,19 +32,15 @@ static struct page *page_idle_get_page(unsigned long pfn) { struct page *page =3D pfn_to_online_page(pfn); - pg_data_t *pgdat; =20 if (!page || !PageLRU(page) || !get_page_unless_zero(page)) return NULL; =20 - pgdat =3D page_pgdat(page); - spin_lock_irq(&pgdat->lru_lock); if (unlikely(!PageLRU(page))) { put_page(page); page =3D NULL; } - spin_unlock_irq(&pgdat->lru_lock); return page; } =20 _