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=-6.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 2DCDBC3404E for ; Wed, 19 Feb 2020 05:22:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 08AAB2465D for ; Wed, 19 Feb 2020 05:22:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Auyp6lhS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726260AbgBSFWc (ORCPT ); Wed, 19 Feb 2020 00:22:32 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:43950 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725819AbgBSFWb (ORCPT ); Wed, 19 Feb 2020 00:22:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=v3wjYvTxIvyqdBjcTZbZ6V6XXTZeeNXrItglyOMcggo=; b=Auyp6lhSbAEYNk7jcncbMkY0Ws XinG1c/KH2WIappKRapF9o4axpn9L8oQskBlHlBLw9XQ0nXbJnkDsqfh2SkyzmQK0YhzpKp/QBFO0 bpEGyHFQ+YA3qxJU00WEU/tiwjkGuEnVYcW0g3zXVubgFDKWaDvoJvN6VkjVPrCo/uQ+QP9jf8QO3 9qiXCqAzx7Awla3qaJlBefBlwM8EQeYBIUB12k8qt69YC/AIm0vwjb3K/41acVQTK6Lg81YYNgtrt gWZkFfEHpJDHCeifbBhNb09jKli8nY0l/0Vau09mO9a0Cb/TiGxAZcwsAaM0Zi6C3GyPPjl+GKcMg Evj5uHjQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j4Hoc-0008Pr-3p; Wed, 19 Feb 2020 05:22:30 +0000 Date: Tue, 18 Feb 2020 21:22:30 -0800 From: Matthew Wilcox To: Dave Chinner 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: <20200219052230.GM24185@bombadil.infradead.org> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-33-willy@infradead.org> <20200219034324.GG10776@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200219034324.GG10776@dread.disaster.area> Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Wed, Feb 19, 2020 at 02:43:24PM +1100, Dave Chinner wrote: > 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 ? I don't think it ensures the GFP_NORETRY | GFP_NOWARN, just the GFP_NOFS part. IOW, we'll still need a readahead_gfp() macro at some point ... I don't want to add that to this already large series though. Michal also wants to kill mapping->gfp_mask, btw.