From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Date: Tue, 14 Apr 2020 08:02:23 -0700 Subject: [Ocfs2-devel] [PATCH v11 15/25] mm: Use memalloc_nofs_save in readahead path In-Reply-To: <20200414150233.24495-1-willy@infradead.org> References: <20200414150233.24495-1-willy@infradead.org> Message-ID: <20200414150233.24495-16-willy@infradead.org> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Andrew Morton Cc: "Matthew Wilcox (Oracle)" , 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 , William Kucharski 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 Reviewed-by: William Kucharski --- mm/readahead.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/mm/readahead.c b/mm/readahead.c index 73cb59ed5cff..3c9a8dd7c56c 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -22,6 +22,7 @@ #include #include #include +#include #include "internal.h" @@ -185,6 +186,18 @@ void page_cache_readahead_unbounded(struct address_space *mapping, }; unsigned long i; + /* + * 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(); + /* * Preallocate as many pages as we will need. */ @@ -229,6 +242,7 @@ void page_cache_readahead_unbounded(struct address_space *mapping, * will then handle the error. */ read_pages(&rac, &page_pool, false); + memalloc_nofs_restore(nofs); } EXPORT_SYMBOL_GPL(page_cache_readahead_unbounded); -- 2.25.1