From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 0A5486B0069 for ; Mon, 6 Feb 2017 13:47:49 -0500 (EST) Received: by mail-wm0-f69.google.com with SMTP id x4so21115311wme.3 for ; Mon, 06 Feb 2017 10:47:48 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id y64si9074981wmy.110.2017.02.06.10.47.47 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 06 Feb 2017 10:47:47 -0800 (PST) Date: Mon, 6 Feb 2017 19:47:43 +0100 From: Michal Hocko Subject: Re: [PATCH 4/6] xfs: use memalloc_nofs_{save,restore} instead of memalloc_noio* Message-ID: <20170206184743.GB20731@dhcp22.suse.cz> References: <20170206140718.16222-1-mhocko@kernel.org> <20170206140718.16222-5-mhocko@kernel.org> <20170206153923.GL2267@bombadil.infradead.org> <20170206174415.GA20731@dhcp22.suse.cz> <20170206183237.GE3580@birch.djwong.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170206183237.GE3580@birch.djwong.org> Sender: owner-linux-mm@kvack.org List-ID: To: "Darrick J. Wong" Cc: Matthew Wilcox , Andrew Morton , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Dave Chinner , djwong@kernel.org, Theodore Ts'o , Chris Mason , David Sterba , Jan Kara , ceph-devel@vger.kernel.org, cluster-devel@redhat.com, linux-nfs@vger.kernel.org, logfs@logfs.org, linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-mtd@lists.infradead.org, reiserfs-devel@vger.kernel.org, linux-ntfs-dev@lists.sourceforge.net, linux-f2fs-devel@lists.sourceforge.net, linux-afs@lists.infradead.org, LKML On Mon 06-02-17 10:32:37, Darrick J. Wong wrote: > On Mon, Feb 06, 2017 at 06:44:15PM +0100, Michal Hocko wrote: > > On Mon 06-02-17 07:39:23, Matthew Wilcox wrote: > > > On Mon, Feb 06, 2017 at 03:07:16PM +0100, Michal Hocko wrote: > > > > +++ b/fs/xfs/xfs_buf.c > > > > @@ -442,17 +442,17 @@ _xfs_buf_map_pages( > > > > bp->b_addr = NULL; > > > > } else { > > > > int retried = 0; > > > > - unsigned noio_flag; > > > > + unsigned nofs_flag; > > > > > > > > /* > > > > * vm_map_ram() will allocate auxillary structures (e.g. > > > > * pagetables) with GFP_KERNEL, yet we are likely to be under > > > > * GFP_NOFS context here. Hence we need to tell memory reclaim > > > > - * that we are in such a context via PF_MEMALLOC_NOIO to prevent > > > > + * that we are in such a context via PF_MEMALLOC_NOFS to prevent > > > > * memory reclaim re-entering the filesystem here and > > > > * potentially deadlocking. > > > > */ > > > > > > This comment feels out of date ... how about: > > > > which part is out of date? > > > > > > > > /* > > > * vm_map_ram will allocate auxiliary structures (eg page > > > * tables) with GFP_KERNEL. If that tries to reclaim memory > > > * by calling back into this filesystem, we may deadlock. > > > * Prevent that by setting the NOFS flag. > > > */ > > > > dunno, the previous wording seems clear enough to me. Maybe little bit > > more chatty than yours but I am not sure this is worth changing. > > I prefer to keep the "...yet we are likely to be under GFP_NOFS..." > wording of the old comment because it captures the uncertainty of > whether or not we actually are already under NOFS. If someone actually > has audited this code well enough to know for sure then yes let's change > the comment, but I haven't gone that far. I believe we can drop the memalloc_nofs_save then as well because either we are called from a potentially dangerous context and thus we are in the nofs scope we we do not need the protection at all. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org