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=-15.7 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 EDA37C433DB for ; Wed, 24 Feb 2021 20:11:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A34B864E20 for ; Wed, 24 Feb 2021 20:11:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234906AbhBXULM (ORCPT ); Wed, 24 Feb 2021 15:11:12 -0500 Received: from mail.kernel.org ([198.145.29.99]:33592 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235399AbhBXUKH (ORCPT ); Wed, 24 Feb 2021 15:10:07 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 66EF164E7A; Wed, 24 Feb 2021 20:09:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1614197366; bh=uC0aIgTXfqlnX4HP+lCV4J82gG1VEkXDb/DDvmEK9/U=; h=Date:From:To:Subject:In-Reply-To:From; b=O8466gW7shCYnPZaCt9fNeH6374dckNJRUCYddXUHLIRxkvYHP5A/70IaDS3/pUko CzmX9D4zo5FZ6cQp4rxZ9xPjDc6RIHsDCVe7gadiTMoJOrkjGxO4R2DcqSK+hysRZK sc59B3PRmTiM22n5pAhy9gzSnEgcpaRMVKnsgXTc= Date: Wed, 24 Feb 2021 12:09:25 -0800 From: Andrew Morton To: akpm@linux-foundation.org, alex.shi@linux.alibaba.com, hannes@cmpxchg.org, hughd@google.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 155/173] mm/compaction: remove rcu_read_lock during page compaction Message-ID: <20210224200925.i6zoXNQy3%akpm@linux-foundation.org> In-Reply-To: <20210224115824.1e289a6895087f10c41dd8d6@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Alex Shi Subject: mm/compaction: remove rcu_read_lock during page compaction isolate_migratepages_block() used rcu_read_lock() with the intention of safeguarding against the mem_cgroup being destroyed concurrently; but its TestClearPageLRU already protects against that. Delete the unnecessary rcu_read_lock() and _unlock(). Hugh Dickins helped on commit log polishing, Thanks! Link: https://lkml.kernel.org/r/1608614453-10739-3-git-send-email-alex.shi@linux.alibaba.com Signed-off-by: Alex Shi Acked-by: Hugh Dickins Cc: Hugh Dickins Cc: Johannes Weiner Signed-off-by: Andrew Morton --- mm/compaction.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) --- a/mm/compaction.c~mm-compaction-remove-rcu_read_lock-during-page-compaction +++ a/mm/compaction.c @@ -995,7 +995,6 @@ isolate_migratepages_block(struct compac if (!TestClearPageLRU(page)) goto isolate_fail_put; - rcu_read_lock(); lruvec = mem_cgroup_page_lruvec(page, pgdat); /* If we already hold the lock, we can skip some rechecking */ @@ -1005,7 +1004,6 @@ isolate_migratepages_block(struct compac compact_lock_irqsave(&lruvec->lru_lock, &flags, cc); locked = lruvec; - rcu_read_unlock(); lruvec_memcg_debug(lruvec, page); @@ -1026,8 +1024,7 @@ isolate_migratepages_block(struct compac SetPageLRU(page); goto isolate_fail_put; } - } else - rcu_read_unlock(); + } /* The whole page is taken off the LRU; skip the tail pages. */ if (PageCompound(page)) _