From: Jan Kara Subject: Re: [PATCH] ext4: Fix delalloc sync hang with journal lock inversion Date: Mon, 2 Jun 2008 12:27:59 +0200 Message-ID: <20080602102759.GG30613@duck.suse.cz> References: <1212154769-16486-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1212154769-16486-2-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1212154769-16486-3-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1212154769-16486-4-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1212154769-16486-5-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1212154769-16486-6-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1212154769-16486-7-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20080602093459.GC30613@duck.suse.cz> <20080602095956.GB9225@skywalker> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: cmm@us.ibm.com, linux-ext4@vger.kernel.org To: "Aneesh Kumar K.V" Return-path: Received: from styx.suse.cz ([82.119.242.94]:35596 "EHLO mail.suse.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755864AbYFBK2B (ORCPT ); Mon, 2 Jun 2008 06:28:01 -0400 Content-Disposition: inline In-Reply-To: <20080602095956.GB9225@skywalker> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon 02-06-08 15:29:56, Aneesh Kumar K.V wrote: > On Mon, Jun 02, 2008 at 11:35:00AM +0200, Jan Kara wrote: > > > BUG_ON(buffer_locked(bh)); > > > if (buffer_dirty(bh)) > > > mpage_add_bh_to_extent(mpd, logical, bh); > > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > > > index 789b6ad..655b8bf 100644 > > > --- a/mm/page-writeback.c > > > +++ b/mm/page-writeback.c > > > @@ -881,7 +881,12 @@ int write_cache_pages(struct address_space *mapping, > > > pagevec_init(&pvec, 0); > > > if (wbc->range_cyclic) { > > > index = mapping->writeback_index; /* Start from prev offset */ > > > - end = -1; > > > + /* > > > + * write only till the specified range_end even in cyclic mode > > > + */ > > > + end = wbc->range_end >> PAGE_CACHE_SHIFT; > > > + if (!end) > > > + end = -1; > > > } else { > > > index = wbc->range_start >> PAGE_CACHE_SHIFT; > > > end = wbc->range_end >> PAGE_CACHE_SHIFT; > > Are you sure you won't break other users of range_cyclic with this > > change? > > > I haven't run any specific test to verify that. The concern was that if > we force cyclic mode for writeout in delalloc we may be starting the > writeout from a different offset than specified and would be writing > more. So the changes was to use the offset specified. A quick look at > the kernel suggested most of them had range_end as 0 with cyclic_mode. > I haven't audited the full kernel. I will do that. Meanwhile if you > think it is risky to make this changes i guess we should drop this > part. But i guess we can keep the below change Hmm, I've just got an idea that it may be better to introduce a new flag for wbc like range_cont and it would mean that we start scan at writeback_index (we use range_start if writeback_index is not set) and end with range_end. That way we don't have to be afraid of interference with other range_cyclic users and in principle, range_cyclic is originally meant for other uses... > + index = mapping->writeback_index; > + if (!range_cyclic) { > + /* > + * We force cyclic write out of pages. If the > + * caller didn't request for range_cyclic update > + * set the writeback_index to what the caller requested. > + */ > + mapping->writeback_index = wbc->range_start >> PAGE_CACHE_SHIFT; > + } Honza -- Jan Kara SUSE Labs, CR