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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 3CDB8C34022 for ; Wed, 19 Feb 2020 03:43:28 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 06FE420801 for ; Wed, 19 Feb 2020 03:43:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 06FE420801 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=fromorbit.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A8D6D6B0006; Tue, 18 Feb 2020 22:43:27 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A3DE46B0007; Tue, 18 Feb 2020 22:43:27 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 92C396B0008; Tue, 18 Feb 2020 22:43:27 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 7773B6B0006 for ; Tue, 18 Feb 2020 22:43:27 -0500 (EST) Received: from smtpin03.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 1472B3499 for ; Wed, 19 Feb 2020 03:43:27 +0000 (UTC) X-FDA: 76505481654.03.chin73_7560dfbfc8a19 X-HE-Tag: chin73_7560dfbfc8a19 X-Filterd-Recvd-Size: 3970 Received: from mail105.syd.optusnet.com.au (mail105.syd.optusnet.com.au [211.29.132.249]) by imf15.hostedemail.com (Postfix) with ESMTP for ; Wed, 19 Feb 2020 03:43:26 +0000 (UTC) Received: from dread.disaster.area (pa49-179-138-28.pa.nsw.optusnet.com.au [49.179.138.28]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id 880BB3A1C09; Wed, 19 Feb 2020 14:43:25 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1j4GGi-0005Z3-WB; Wed, 19 Feb 2020 14:43:25 +1100 Date: Wed, 19 Feb 2020 14:43:24 +1100 From: Dave Chinner To: Matthew Wilcox Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, ocfs2-devel@oss.oracle.com, linux-xfs@vger.kernel.org, Cong Wang , Michal Hocko Subject: Re: [PATCH v6 19/19] mm: Use memalloc_nofs_save in readahead path Message-ID: <20200219034324.GG10776@dread.disaster.area> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-33-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200217184613.19668-33-willy@infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=X6os11be c=1 sm=1 tr=0 a=zAxSp4fFY/GQY8/esVNjqw==:117 a=zAxSp4fFY/GQY8/esVNjqw==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=l697ptgUJYAA:10 a=JfrnYn6hAAAA:8 a=pGLkceISAAAA:8 a=iox4zFpeAAAA:8 a=7-415B0cAAAA:8 a=EUu7BJ-CshYY2WUz2RUA:9 a=Ins956pMss7IOATM:21 a=TqZTP-Om_uFHSJHF:21 a=CjuIK1q_8ugA:10 a=1CNFftbPRP8L7MoqJWF3:22 a=WzC6qhA0u3u7Ye7llzcV:22 a=biEYGPWJfzWAr4FL6Ov7:22 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: On Mon, Feb 17, 2020 at 10:46:13AM -0800, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" > > Ensure that memory allocations in the readahead path do not attempt to > reclaim file-backed pages, which could lead to a deadlock. It is > possible, though unlikely this is the root cause of a problem observed > by Cong Wang. > > Signed-off-by: Matthew Wilcox (Oracle) > Reported-by: Cong Wang > Suggested-by: Michal Hocko > --- > mm/readahead.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/mm/readahead.c b/mm/readahead.c > index 94d499cfb657..8f9c0dba24e7 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -22,6 +22,7 @@ > #include > #include > #include > +#include > > #include "internal.h" > > @@ -174,6 +175,18 @@ void page_cache_readahead_limit(struct address_space *mapping, > ._nr_pages = 0, > }; > > + /* > + * Partway through the readahead operation, we will have added > + * locked pages to the page cache, but will not yet have submitted > + * them for I/O. Adding another page may need to allocate memory, > + * which can trigger memory reclaim. Telling the VM we're in > + * the middle of a filesystem operation will cause it to not > + * touch file-backed pages, preventing a deadlock. Most (all?) > + * filesystems already specify __GFP_NOFS in their mapping's > + * gfp_mask, but let's be explicit here. > + */ > + unsigned int nofs = memalloc_nofs_save(); > + So doesn't this largely remove the need for all the gfp flag futzing in the readahead path? i.e. almost all readahead allocations are now going to be GFP_NOFS | GFP_NORETRY | GFP_NOWARN ? If so, shouldn't we just strip all the gfp flags and masking out of the readahead path altogether? Cheers, Dave. -- Dave Chinner david@fromorbit.com