Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758403AbZDNSVB (ORCPT ); Tue, 14 Apr 2009 14:21:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757201AbZDNSUv (ORCPT ); Tue, 14 Apr 2009 14:20:51 -0400 Received: from brick.kernel.dk ([93.163.65.50]:36808 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754850AbZDNSUv (ORCPT ); Tue, 14 Apr 2009 14:20:51 -0400 Date: Tue, 14 Apr 2009 20:20:49 +0200 From: Jens Axboe To: Theodore Tso Cc: Nikanth Karthikesan , Neil Brown , linux-kernel@vger.kernel.org, Chris Mason , Andrew Morton , Dave Kleikamp , xfs-masters@oss.sgi.com Subject: Re: [PATCH 0/6] Handle bio_alloc failure Message-ID: <20090414182049.GI5178@kernel.dk> References: <200904141636.26557.knikanth@novell.com> <20090414111838.GG5178@kernel.dk> <200904141711.20378.knikanth@suse.de> <20090414181632.GI955@mit.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090414181632.GI955@mit.edu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1529 Lines: 37 On Tue, Apr 14 2009, Theodore Tso wrote: > On Tue, Apr 14, 2009 at 05:11:19PM +0530, Nikanth Karthikesan wrote: > > On Tuesday 14 April 2009 16:48:38 Jens Axboe wrote: > > > > > > It will not fail as long as __GFP_WAIT is set, which it is for all 6 of > > > your patches. > > Um, before we take out the checks, can we please make sure this is a > guaranteed, documented behaviour? In include/linux/page_alloc.h, > __GFP_NOFAIL is documented as "will never fail", but it says > absolutely nothing about __GFP_WAIT. > > Some day, someone will create a static checker that will flag warnings > when people fail to check for allocation failures, and it would be > good if the formal semantics for __GFP_WAIT, and hence for GFP_NOFS, > GFP_KERNEL, and GFP_USER, et. al. are defined. > > We have code in fs/jbd2/transaction.c that calls kzalloc with > GFP_NOFS|__GFP_NOFAIL, since I and many other people had the > assumption that without __GFP_NOFAIL, an GFP_NOFS allocation could > very well fail. > > Or is this special-case behaviour which bio_alloc() guarantees, but > not necessarily any other allocation function? It's a bio_alloc() guarantee, it uses a mempool backing. And if you use a mempool backing, any allocation that can wait will always be satisfied. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/