Return-Path: linux-nfs-owner@vger.kernel.org Received: from mail-pd0-f182.google.com ([209.85.192.182]:59670 "EHLO mail-pd0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751090AbaLQO6g (ORCPT ); Wed, 17 Dec 2014 09:58:36 -0500 Received: by mail-pd0-f182.google.com with SMTP id p10so16224526pdj.41 for ; Wed, 17 Dec 2014 06:58:36 -0800 (PST) Date: Wed, 17 Dec 2014 06:58:32 -0800 From: Omar Sandoval To: Christoph Hellwig , Al Viro Cc: Jan Kara , Andrew Morton , Trond Myklebust , David Sterba , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/8] swap: lock i_mutex for swap_writepage direct_IO Message-ID: <20141217145832.GA3497@mew> References: <20141215162705.GA23887@quack.suse.cz> <20141215165615.GA19041@infradead.org> <20141215221100.GA4637@mew> <20141216083543.GA32425@infradead.org> <20141216085624.GA25256@mew> <20141217080610.GA20335@infradead.org> <20141217082020.GH22149@ZenIV.linux.org.uk> <20141217082437.GA9301@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20141217082437.GA9301@infradead.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, Dec 17, 2014 at 12:24:37AM -0800, Christoph Hellwig wrote: > On Wed, Dec 17, 2014 at 08:20:21AM +0000, Al Viro wrote: > > Where the hell would those other references come from? We open the damn > > thing in sys_swapon(), never put it into descriptor tables, etc. and > > the only reason why we use filp_close() instead of fput() is that we > > would miss ->flush() otherwise. > > > > Said that, why not simply *open* it with O_DIRECT to start with and be done > > with that? It's not as if those guys came preopened by caller - swapon(2) > > gets a pathname and does opening itself. > > Oops, should have dug deeper into the code. For some reason I assumed > the fd is passed in from userspace. > > The suggestion from Al is much better, given that we never do normal > I/O on the swapfile, just the bmap + direct bio submission which I hope > could go away in favor of the direct I/O variant in the long run. See my previous message. If we use O_DIRECT on the original open, then filesystems that implement bmap but not direct_IO will no longer work. These are the ones that I found in my tree: adfs befs bfs ecryptfs efs freevxfs hpfs isofs minix ntfs omfs qnx4 qnx6 sysv ufs Several of these are read only, and I can't imagine that anyone is using a swapfile on any of the rest, but if someone is, this would be a regression, wouldn't it? -- Omar