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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 7C568C33CA2 for ; Fri, 10 Jan 2020 07:38:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5058120673 for ; Fri, 10 Jan 2020 07:38:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578641910; bh=rtOHPb5VBELvsqUwFnzqmBRxgpxFX3NiQM661iA+jMw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ddjuTb45jjm0CR1VWYKtRxPMhIRb9UREN8a84Plori6VGcJU6qYKMHvcvSOqQfHb3 4O0hWnGGT7mLOaHifj4++kDQRssyWqtrYuwyrCVao5pPjaWYhpKyssywULMhcE0AtH 7RBhf1eOLDX2kYcM28Fxt0hSPAC64Zznen76XQcg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726716AbgAJHi3 (ORCPT ); Fri, 10 Jan 2020 02:38:29 -0500 Received: from mail-wm1-f68.google.com ([209.85.128.68]:39380 "EHLO mail-wm1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726551AbgAJHi2 (ORCPT ); Fri, 10 Jan 2020 02:38:28 -0500 Received: by mail-wm1-f68.google.com with SMTP id 20so853968wmj.4 for ; Thu, 09 Jan 2020 23:38:27 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=ZjWwBZ88Q84uyiPwE+9hZtJZXGqPOEuXwHPuM2hDV6M=; b=kvkgThAS+lgsmfQvEd8irKxvG0HKux2yPp6IGqBXm3bEFBtwjTJ54Y2EtQPvGAjdJx 1UJfyNoPpmhb2DqxqD7zfC8JAArX7WRUZUdbAVwM17Ze8etGDaTXRfWqabNLmVBS5xy+ r/G7iOjBCb2/d3UjkXI8sjrRPvLXoY221nRnPSDJRV65Ksy885sLUX9FqNjuHTtq1ZS+ YqkmXvBKiDhfDmufmdQ7DOLAP8MohNCDgb5mPdvbti/I2FviDVF3Ws/JhJI2ifpMR2Is 9hUf9jhCa9BZaDQsL9sM9Bush5TayxJLH2edLK8bWnc/OwufNd4wgqiyIbMZ4FI5zgmi bdbw== X-Gm-Message-State: APjAAAVlOYJXHxO8Y2zVX2qK31VYlCINLzoST2xLHDjIxX7sq53ybZYu LNOOQ/pUkdKN3Z9qeu4lu/U= X-Google-Smtp-Source: APXvYqxp1oB3tJAXijtVgqdDR+/kcuIcgwR9w6Y7iWy6vogK8Ly5w8bDeGZ3IGRlq4G6f6TF+Eu93Q== X-Received: by 2002:a05:600c:2c08:: with SMTP id q8mr2409649wmg.45.1578641906642; Thu, 09 Jan 2020 23:38:26 -0800 (PST) Received: from localhost (ip-37-188-146-105.eurotel.cz. [37.188.146.105]) by smtp.gmail.com with ESMTPSA id u24sm1247888wml.10.2020.01.09.23.38.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Jan 2020 23:38:25 -0800 (PST) Date: Fri, 10 Jan 2020 08:38:22 +0100 From: Michal Hocko To: Cong Wang Cc: linux-kernel@vger.kernel.org, Andrew Morton , linux-mm@kvack.org, Mel Gorman , Vlastimil Babka Subject: Re: [PATCH] mm: avoid blocking lock_page() in kcompactd Message-ID: <20200110073822.GC29802@dhcp22.suse.cz> References: <20200109225646.22983-1-xiyou.wangcong@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200109225646.22983-1-xiyou.wangcong@gmail.com> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [CC Mel and Vlastimil] On Thu 09-01-20 14:56:46, Cong Wang wrote: > We observed kcompactd hung at __lock_page(): > > INFO: task kcompactd0:57 blocked for more than 120 seconds. > Not tainted 4.19.56.x86_64 #1 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > kcompactd0 D 0 57 2 0x80000000 > Call Trace: > ? __schedule+0x236/0x860 > schedule+0x28/0x80 > io_schedule+0x12/0x40 > __lock_page+0xf9/0x120 > ? page_cache_tree_insert+0xb0/0xb0 > ? update_pageblock_skip+0xb0/0xb0 > migrate_pages+0x88c/0xb90 > ? isolate_freepages_block+0x3b0/0x3b0 > compact_zone+0x5f1/0x870 > kcompactd_do_work+0x130/0x2c0 > ? __switch_to_asm+0x35/0x70 > ? __switch_to_asm+0x41/0x70 > ? kcompactd_do_work+0x2c0/0x2c0 > ? kcompactd+0x73/0x180 > kcompactd+0x73/0x180 > ? finish_wait+0x80/0x80 > kthread+0x113/0x130 > ? kthread_create_worker_on_cpu+0x50/0x50 > ret_from_fork+0x35/0x40 > > which faddr2line maps to: > > migrate_pages+0x88c/0xb90: > lock_page at include/linux/pagemap.h:483 > (inlined by) __unmap_and_move at mm/migrate.c:1024 > (inlined by) unmap_and_move at mm/migrate.c:1189 > (inlined by) migrate_pages at mm/migrate.c:1419 > > Sometimes kcompactd eventually got out of this situation, sometimes not. What does this mean exactly? Who is holding the page lock? > I think for memory compaction, it is a best effort to migrate the pages, > so it doesn't have to wait for I/O to complete. It is fine to call > trylock_page() here, which is pretty much similar to > buffer_migrate_lock_buffers(). > > Given MIGRATE_SYNC_LIGHT is used on compaction path, just relax the > check for it. The exact definition of MIGRATE_SYNC_LIGHT is a bit fuzzy but bailing out on the page lock sounds too early to me. So far we have tried to block on everything but the writeback which can take a lot of time. > Cc: Andrew Morton > Cc: Michal Hocko > Cc: linux-mm@kvack.org > Signed-off-by: Cong Wang > --- > mm/migrate.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 86873b6f38a7..df60026779d2 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1010,7 +1010,8 @@ static int __unmap_and_move(struct page *page, struct page *newpage, > bool is_lru = !__PageMovable(page); > > if (!trylock_page(page)) { > - if (!force || mode == MIGRATE_ASYNC) > + if (!force || mode == MIGRATE_ASYNC > + || mode == MIGRATE_SYNC_LIGHT) > goto out; > > /* > -- > 2.21.1 > -- Michal Hocko SUSE Labs