From: Chris Mason Subject: Re: [PATCH] jbd jbd2: fix dio write returning EIO whentry_to_release_page fails Date: Tue, 05 Aug 2008 12:17:35 -0400 Message-ID: <1217953055.7899.11.camel@think.oraclecorp.com> References: <6.0.0.20.2.20080804185338.03bcd488@172.19.0.2> <20080804145047.04794bf3.akpm@linux-foundation.org> <1217907353.7611.39.camel@think.oraclecorp.com> <6.0.0.20.2.20080805134429.044569a0@172.19.0.2> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Andrew Morton , cmm@us.ibm.com, jack@suse.cz, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Hisashi Hifumi Return-path: Received: from agminet01.oracle.com ([141.146.126.228]:56536 "EHLO agminet01.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761351AbYHERpl (ORCPT ); Tue, 5 Aug 2008 13:45:41 -0400 In-Reply-To: <6.0.0.20.2.20080805134429.044569a0@172.19.0.2> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, 2008-08-05 at 13:51 +0900, Hisashi Hifumi wrote: > >> > > >> > diff -Nrup linux-2.6.27-rc1.org/fs/jbd/transaction.c > >linux-2.6.27-rc1/fs/jbd/transaction.c > >> > --- linux-2.6.27-rc1.org/fs/jbd/transaction.c 2008-07-29 > >19:28:47.000000000 +0900 > >> > +++ linux-2.6.27-rc1/fs/jbd/transaction.c 2008-07-29 20:40:12.000000000 +0900 > >> > @@ -1764,6 +1764,12 @@ int journal_try_to_free_buffers(journal_ > >> > */ > >> > if (ret == 0 && (gfp_mask & __GFP_WAIT) && (gfp_mask & __GFP_FS)) { > >> > journal_wait_for_transaction_sync_data(journal); > >> > + > >> > + bh = head; > >> > + do { > >> > + while (atomic_read(&bh->b_count)) > >> > + schedule(); > >> > + } while ((bh = bh->b_this_page) != head); > >> > ret = try_to_free_buffers(page); > >> > } > >> > >> The loop is problematic. If the scheduler decides to keep running this > >> task then we have a busy loop. If this task has realtime policy then > >> it might even lock up the kernel. > >> > > > >ocfs2 calls journal_try_to_free_buffers too, looping on b_count might > >not be the best idea there either. > > > >This code gets called from releasepage, which is used other places than > >the O_DIRECT invalidation paths, I'd be worried about performance > >problems here. > > > > try_to_release_page has gfp_mask parameter. So when try_to_releasepage > is called from performance sensitive part, gfp_mask should not be set. > b_count check loop is inside of (gfp_mask & __GFP_WAIT) && (gfp_mask & __GFP_FS) check. Looks like try_to_free_pages will go into releasepage with wait & fs both set. This kind of change would make me very nervous. -chris