Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755171Ab0GFHzl (ORCPT ); Tue, 6 Jul 2010 03:55:41 -0400 Received: from rcsinet10.oracle.com ([148.87.113.121]:62847 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751194Ab0GFHzk (ORCPT ); Tue, 6 Jul 2010 03:55:40 -0400 Message-ID: <4C32E152.1090902@oracle.com> Date: Tue, 06 Jul 2010 15:54:58 +0800 From: Tao Ma User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.9) Gecko/20100317 Thunderbird/3.0.4 MIME-Version: 1.0 To: Dave Chinner , Linus Torvalds , Linux Kernel , ocfs2-devel@oss.oracle.com, Dave Chinner , Christoph Hellwig , Mark Fasheh , Joel Becker Subject: Re: [PATCH 1/2] ocfs2: Zero the tail cluster when extending past i_size v2 References: <20100628173529.GA10573@mail.oracle.com> <20100629002421.GY6590@dastard> <20100629005403.GC24343@mail.oracle.com> <20100629015615.GZ6590@dastard> <20100629020420.GE24343@mail.oracle.com> <20100629022757.GA6590@dastard> <20100629071817.GA4150@mail.oracle.com> <20100702224912.GC5800@mail.oracle.com> <20100703213219.GB21262@mail.oracle.com> <4C3156D0.5090001@oracle.com> <20100706071741.GF13023@mail.oracle.com> In-Reply-To: <20100706071741.GF13023@mail.oracle.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: acsmt354.oracle.com [141.146.40.154] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090208.4C32E15B.0006:SCFMA4539814,ss=1,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3799 Lines: 97 Hi Joel, On 07/06/2010 03:17 PM, Joel Becker wrote: > On Mon, Jul 05, 2010 at 11:51:44AM +0800, Tao Ma wrote: >>> + /* >>> + * If tail_blkno is in the cluster past i_size, we don't need >>> + * to touch the cluster containing i_size at all. >>> + */ >>> + tail_cpos = i_size_read(inode)>> osb->s_clustersize_bits; >>> + if (ocfs2_blocks_to_clusters(inode->i_sb, tail_blkno)> tail_cpos) >>> + tail_cpos = ocfs2_blocks_to_clusters(inode->i_sb, >>> + tail_blkno); >> Can we always set tail_cpos in one line? >> tail_cpos = ocfs2_blocks_to_clusters(inode->i_sb, tail_blkno)? >> tail_cpos is either the same cluster as i_size or the next cluster >> and both works for tail_blkno I guess? > > I had the same thought on Friday, but the current version passes > testing and I was wary of changing that. ok, so as you wish. > >>> + /* Is there a cluster to zero? */ >>> + if (!p_cpos) >>> + goto out; >> For unwritten extent, we also need to clear the pages? If yes, the >> solution doesn't complete if we have 2 unwritten extent, one >> contains i_size while one passes i_size. Here we only clear the >> pages for the 1st unwritten extent and leave the 2nd one untouched. > > We probably don't need to zero unwritten extents. We cannot > have an extent past i_size, can we? we can. AFAICS, ocfs2_change_file_space will allocate unwritten extents and does't change i_size. > >> From here to the call of CoW is a bit hard to understand. In 'if', >> num_clusters is set for CoW and in 'else', blocks_to_zero is set. So >> it isn't easy for the reader to tell why these 2 clauses are setting >> different values. So how about my code below? It looks more >> straightforward I think. >>> + if ((tail_cpos + num_clusters)> pos_cpos) { >>> + num_clusters = pos_cpos - tail_cpos; >>> + if (pos_blkno> >>> + ocfs2_clusters_to_blocks(inode->i_sb, pos_cpos)) >>> + num_clusters += 1; >>> + } else { >>> + blocks_to_zero = >>> + ocfs2_clusters_to_blocks(inode->i_sb, >>> + tail_cpos + num_clusters); >>> + blocks_to_zero -= tail_blkno; >>> + } >>> + >>> + /* Now CoW the clusters we're about to zero */ >>> + if (ext_flags& OCFS2_EXT_REFCOUNTED) { >>> + rc = ocfs2_refcount_cow(inode, di_bh, tail_cpos, >>> + num_clusters, UINT_MAX); >>> + if (rc) { >>> + mlog_errno(rc); >>> + goto out; >>> + } >>> + } >> /* Decrease blocks_to_zero if there is some hole after extent */ >> if (tail_cpos + num_clusters<= pos_cpos) { >> blocks_to_zero = >> ocfs2_clusters_to_blocks(inode->i_sb, >> tail_cpos + num_clusters); >> blocks_to_zero -= tail_blkno; >> } > > Not a bad split-out here. > >> /* Now CoW if we have some refcounted clusters. */ >> if (ext_flags& OCFS2_EXT_REFCOUNTED) { >> /* >> * We add one more cluster here since it will be >> * written shortly and if the pos_blkno isn't aligned >> * to the cluster size, we have to zero the blocks >> * before it. >> */ >> if (tail_cpos + num_clusters> pos_cpos) >> num_clusters = pos_cpos - tail_cpos + 1; > > But you dropped the check for pos_blkno alignment. > Unconditionally adding the +1 doesn't seem like a good idea. You can add it as you wish. I just thought that you add one more extra cluster if pos_blkno isn't aligned so as to zero blocks in [pos_cpos_start_block, pos_blkno). But As I said in the comments, you will soon write pos_blkno(it also needs to be CoW since it is within this refcounted extent), so if we can CoW it out now, maybe we have a chance to not call ocfs2_refcount_cow later. Regards, Tao -- 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/