From: Hisashi Hifumi Subject: Re: [PATCH] jbd jbd2: fix dio write returning EIO whentry_to_release_page fails Date: Tue, 05 Aug 2008 13:51:41 +0900 Message-ID: <6.0.0.20.2.20080805134429.044569a0@172.19.0.2> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: cmm@us.ibm.com, jack@suse.cz, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Chris Mason , Andrew Morton Return-path: In-Reply-To: <1217907353.7611.39.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> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org >> > >> > 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.