Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752210Ab0FOEjA (ORCPT ); Tue, 15 Jun 2010 00:39:00 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:43950 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751040Ab0FOEiz (ORCPT ); Tue, 15 Jun 2010 00:38:55 -0400 Date: Mon, 14 Jun 2010 21:37:32 -0700 From: Andrew Morton To: Rik van Riel Cc: Dave Chinner , Mel Gorman , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Chris Mason , Nick Piggin , Johannes Weiner , Christoph Hellwig , KAMEZAWA Hiroyuki Subject: Re: [PATCH 11/12] vmscan: Write out dirty pages in batch Message-Id: <20100614213732.034b4a13.akpm@linux-foundation.org> In-Reply-To: <4C16FCAE.4050607@redhat.com> References: <1276514273-27693-1-git-send-email-mel@csn.ul.ie> <1276514273-27693-12-git-send-email-mel@csn.ul.ie> <20100614231144.GG6590@dastard> <20100614162143.04783749.akpm@linux-foundation.org> <20100615003943.GK6590@dastard> <4C16D46D.3020302@redhat.com> <20100614184544.32b1c371.akpm@linux-foundation.org> <4C16FCAE.4050607@redhat.com> X-Mailer: Sylpheed 2.7.1 (GTK+ 2.18.9; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2630 Lines: 60 On Tue, 15 Jun 2010 00:08:14 -0400 Rik van Riel wrote: > On 06/14/2010 09:45 PM, Andrew Morton wrote: > > On Mon, 14 Jun 2010 21:16:29 -0400 Rik van Riel wrote: > > > >> Would it be hard to add a "please flush this file" > >> way to call the filesystem flushing threads? > > > > Passing the igrab()bed inode into the flusher threads would fix the > > iput_final() problems, as long as the alloc_pages() caller never blocks > > indefinitely waiting for the work which the flusher threads are doing. > > > > Otherwise we get (very hard-to-hit) deadlocks where the alloc_pages() > > caller holds VFS locks and is waiting for the flusher threads while all > > the flusher threads are stuck under iput_final() waiting for those VFS > > locks. > > > > That's fixable by not using igrab()/iput(). You can use lock_page() to > > pin the address_space. Pass the address of the locked page across to > > the flusher threads so they don't try to lock it a second time, or just > > use trylocking on that writeback path or whatever. > > Any thread that does not have __GFP_FS set in its gfp_mask > cannot wait for the flusher to complete. This is regardless > of the mechanism used to kick the flusher. mm... kinda. A bare order-zero __GFP_WAIT allocation can still wait forever, afaict. > Then again, those threads cannot call ->writepage today > either, so we should be fine keeping that behaviour. I'm not sure. iput_final() can take a lot of locks, both VFS and heaven knows what within the individual filesystems. Is it the case that all allocations which occur under all of those locks is always !__GFP_FS? Hard to say... > Threads that do have __GFP_FS in their gfp_mask can wait > for the flusher in various ways. Maybe the lock_page() > method can be simplified by having the flusher thread > unlock the page the moment it gets it, and then run the > normal flusher code? Well, _something_ has to pin the address_space. A single locked page will do. > The pageout code (in shrink_page_list) already unlocks > the page anyway before putting it back on the relevant > LRU list. It would be easy enough to skip that unlock > and let the flusher thread take care of it. Once that page is unlocked, we can't touch *mapping - its inode can be concurrently reclaimed. Although I guess the technique in handle_write_error() can be reused. -- 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/