From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755028AbWL2Py1 (ORCPT ); Fri, 29 Dec 2006 10:54:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755040AbWL2Py1 (ORCPT ); Fri, 29 Dec 2006 10:54:27 -0500 Received: from sorrow.cyrius.com ([65.19.161.204]:42473 "EHLO sorrow.cyrius.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755024AbWL2Py0 (ORCPT ); Fri, 29 Dec 2006 10:54:26 -0500 Date: Fri, 29 Dec 2006 16:54:04 +0100 From: Martin Michlmayr To: Stephen Clark Cc: Linus Torvalds , Segher Boessenkool , David Miller , nickpiggin@yahoo.com.au, kenneth.w.chen@intel.com, guichaz@yahoo.fr, hugh@veritas.com, Linux Kernel Mailing List , ranma@tdiedrich.de, gordonfarquharson@gmail.com, Andrew Morton , a.p.zijlstra@chello.nl, arjan@infradead.org, andrei.popa@i-neo.ro Subject: Re: Ok, explained.. (was Re: [PATCH] mm: fix page_mkclean_one) Message-ID: <20061229155404.GL2062@deprecation.cyrius.com> References: <20061228114517.3315aee7.akpm@osdl.org> <20061228.143815.41633302.davem@davemloft.net> <3d6d8711f7b892a11801d43c5996ebdf@kernel.crashing.org> <20061229140822.GH2062@deprecation.cyrius.com> <4595318B.10102@seclark.us> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4595318B.10102@seclark.us> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Stephen Clark [2006-12-29 10:17]: > >It works for me now, both your testcase as well as an installation of > >Debian on this ARM device. I manually applied the patch to 2.6.19. > > Can you post a diff against 2.6.19? --- a/mm/page-writeback.c 2006-11-29 21:57:37.000000000 +0000 +++ b/mm/page-writeback.c 2006-12-29 11:02:55.555147896 +0000 @@ -893,16 +893,45 @@ { struct address_space *mapping = page_mapping(page); - if (mapping) { + if (mapping && mapping_cap_account_dirty(mapping)) { + /* + * Yes, Virginia, this is indeed insane. + * + * We use this sequence to make sure that + * (a) we account for dirty stats properly + * (b) we tell the low-level filesystem to + * mark the whole page dirty if it was + * dirty in a pagetable. Only to then + * (c) clean the page again and return 1 to + * cause the writeback. + * + * This way we avoid all nasty races with the + * dirty bit in multiple places and clearing + * them concurrently from different threads. + * + * Note! Normally the "set_page_dirty(page)" + * has no effect on the actual dirty bit - since + * that will already usually be set. But we + * need the side effects, and it can help us + * avoid races. + * + * We basically use the page "master dirty bit" + * as a serialization point for all the different + * threds doing their things. + * + * FIXME! We still have a race here: if somebody + * adds the page back to the page tables in + * between the "page_mkclean()" and the "TestClearPageDirty()", + * we might have it mapped without the dirty bit set. + */ + if (page_mkclean(page)) + set_page_dirty(page); if (TestClearPageDirty(page)) { - if (mapping_cap_account_dirty(mapping)) { - page_mkclean(page); - dec_zone_page_state(page, NR_FILE_DIRTY); - } + dec_zone_page_state(page, NR_FILE_DIRTY); return 1; } return 0; - } + } return TestClearPageDirty(page); } EXPORT_SYMBOL(clear_page_dirty_for_io); -- Martin Michlmayr http://www.cyrius.com/