From patchwork Mon Feb 17 18:46:13 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Matthew Wilcox (Oracle)" X-Patchwork-Id: 11387443 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D6EB9138D for ; Mon, 17 Feb 2020 18:49:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B7A2322525 for ; Mon, 17 Feb 2020 18:49:34 +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="by4S+Hud" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729982AbgBQStb (ORCPT ); Mon, 17 Feb 2020 13:49:31 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:48022 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729541AbgBQSqR (ORCPT ); Mon, 17 Feb 2020 13:46:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender :Reply-To:Content-Type:Content-ID:Content-Description; bh=cAMSPd0G1UKWpX2DYFJf6s7OiGA49hD2HbMDxjJorXI=; b=by4S+HudkubDhJMCqtucpyVJYH +51vmgnEamWn4YLYYEZStDwKyEo7sFXwK4JJdAikHQvi4wLGlUSzXVwrHvqZl/MySIOs8F5a2WJwg XIC4jIfdvSmaswvzMJCrYgtlaHeyHkoWBbkfLI+cq0LKAfekELxKJuW2r5kH6lfA10y22KNnM6zfi ABc5R3/1PqE7XKHVvbCJfr+uDNcwVzXB+QbTzZRmD5Pdi0pTvxwkJ4tKsgOwVwk2HcCTpoV35pv9s djzxIqYl6imCZ8V2jkfCkF3tDtbbHHT1Z6U79+n9yzetFHJprdKqv8EXklKtWyOuHiXMo2ovVvM2n 1x9ivLVQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j3lPM-0005EA-Is; Mon, 17 Feb 2020 18:46:16 +0000 From: Matthew Wilcox To: linux-fsdevel@vger.kernel.org Cc: "Matthew Wilcox (Oracle)" , 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: [PATCH v6 19/19] mm: Use memalloc_nofs_save in readahead path Date: Mon, 17 Feb 2020 10:46:13 -0800 Message-Id: <20200217184613.19668-33-willy@infradead.org> X-Mailer: git-send-email 2.21.1 In-Reply-To: <20200217184613.19668-1-willy@infradead.org> References: <20200217184613.19668-1-willy@infradead.org> MIME-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org 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(); + /* * Preallocate as many pages as we will need. */ @@ -227,6 +240,7 @@ void page_cache_readahead_limit(struct address_space *mapping, if (readahead_count(&rac)) read_pages(&rac, &page_pool); BUG_ON(!list_empty(&page_pool)); + memalloc_nofs_restore(nofs); } EXPORT_SYMBOL_GPL(page_cache_readahead_limit);