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 A8B8AC48BE8 for ; Wed, 16 Jun 2021 01:23:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5E34061356 for ; Wed, 16 Jun 2021 01:23:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5E34061356 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 0583F6B007D; Tue, 15 Jun 2021 21:23:45 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 007496B007E; Tue, 15 Jun 2021 21:23:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DC5086B0080; Tue, 15 Jun 2021 21:23:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0078.hostedemail.com [216.40.44.78]) by kanga.kvack.org (Postfix) with ESMTP id A57BC6B007D for ; Tue, 15 Jun 2021 21:23:44 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 42F21824999B for ; Wed, 16 Jun 2021 01:23:44 +0000 (UTC) X-FDA: 78257839968.21.95EDBC7 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf04.hostedemail.com (Postfix) with ESMTP id C5D2E371 for ; Wed, 16 Jun 2021 01:23:37 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id EEF6561159; Wed, 16 Jun 2021 01:23:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1623806623; bh=JouAOaKCTdqY1DBVgWnTWERrrO0w/43jM+7ztemVfbM=; h=Date:From:To:Subject:In-Reply-To:From; b=QVjUdCIX3xbgtrEmftKbAt4lPXwC4Jo+fPJTEBRR+jiSmn0U9/61AStAo47JIEPPu 4bvF7yx84vd4cszrMY9BbsacWT8l8PGeJfCWvJXeGeDUZRd76kiECIE5sMJ0KIE7kI WVtMRrahERtXT+rXLsQ91LzSasNaB3HlWAnyNf4c= Date: Tue, 15 Jun 2021 18:23:42 -0700 From: Andrew Morton To: akpm@linux-foundation.org, gavin.dg@linux.alibaba.com, hughd@google.com, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, stable@vger.kernel.org, torvalds@linux-foundation.org, willy@infradead.org, xuyu@linux.alibaba.com Subject: [patch 10/18] mm, thp: use head page in __migration_entry_wait() Message-ID: <20210616012342.r-f9_qYFs%akpm@linux-foundation.org> In-Reply-To: <20210615182248.9a0ba90e8e66b9f4a53c0d23@linux-foundation.org> User-Agent: s-nail v14.8.16 Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=QVjUdCIX; dmarc=none; spf=pass (imf04.hostedemail.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-Rspamd-Server: rspam02 X-Stat-Signature: tgyfd4mx5k1b5o4qhuhqzay77wgrrmhi X-Rspamd-Queue-Id: C5D2E371 X-HE-Tag: 1623806617-186824 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: From: Xu Yu Subject: mm, thp: use head page in __migration_entry_wait() We notice that hung task happens in a corner but practical scenario when CONFIG_PREEMPT_NONE is enabled, as follows. Process 0 Process 1 Process 2..Inf split_huge_page_to_list unmap_page split_huge_pmd_address __migration_entry_wait(head) __migration_entry_wait(tail) remap_page (roll back) remove_migration_ptes rmap_walk_anon cond_resched Where __migration_entry_wait(tail) is occurred in kernel space, e.g., copy_to_user in fstat, which will immediately fault again without rescheduling, and thus occupy the cpu fully. When there are too many processes performing __migration_entry_wait on tail page, remap_page will never be done after cond_resched. This makes __migration_entry_wait operate on the compound head page, thus waits for remap_page to complete, whether the THP is split successfully or roll back. Note that put_and_wait_on_page_locked helps to drop the page reference acquired with get_page_unless_zero, as soon as the page is on the wait queue, before actually waiting. So splitting the THP is only prevented for a brief interval. Link: https://lkml.kernel.org/r/b9836c1dd522e903891760af9f0c86a2cce987eb.1623144009.git.xuyu@linux.alibaba.com Fixes: ba98828088ad ("thp: add option to setup migration entries during PMD split") Suggested-by: Hugh Dickins Signed-off-by: Gang Deng Signed-off-by: Xu Yu Acked-by: Kirill A. Shutemov Acked-by: Hugh Dickins Cc: Matthew Wilcox Cc: Signed-off-by: Andrew Morton --- mm/migrate.c | 1 + 1 file changed, 1 insertion(+) --- a/mm/migrate.c~mm-thp-use-head-page-in-__migration_entry_wait +++ a/mm/migrate.c @@ -295,6 +295,7 @@ void __migration_entry_wait(struct mm_st goto out; page = migration_entry_to_page(entry); + page = compound_head(page); /* * Once page cache replacement of page migration started, page_count _