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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 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-Disposition: inline In-Reply-To: <20200219034324.GG10776@dread.disaster.area> X-Headers-End: 1j4Hoq-007v9D-PR Subject: Re: [f2fs-dev] [PATCH v6 19/19] mm: Use memalloc_nofs_save in readahead path X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-xfs@vger.kernel.org, Michal Hocko , linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, linux-mm@kvack.org, ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org, Cong Wang , linux-ext4@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net 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. _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel