From: "Aneesh Kumar K.V" Subject: Re: [PATCH updated] ext4: Fix file fragmentation during large file write. Date: Thu, 16 Oct 2008 13:20:54 +0530 Message-ID: <20081016075054.GC19480@skywalker> References: <1223661776-20098-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1224103260.6938.45.camel@think.oraclecorp.com> <1224114692.6938.48.camel@think.oraclecorp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: cmm@us.ibm.com, tytso@mit.edu, sandeen@redhat.com, akpm@linux-foundation.org, hch@infradead.org, steve@chygwyn.com, npiggin@suse.de, mpatocka@redhat.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org To: Chris Mason Return-path: Content-Disposition: inline In-Reply-To: <1224114692.6938.48.camel@think.oraclecorp.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Wed, Oct 15, 2008 at 07:51:32PM -0400, Chris Mason wrote: > On Wed, 2008-10-15 at 16:41 -0400, Chris Mason wrote: > > On Fri, 2008-10-10 at 23:32 +0530, Aneesh Kumar K.V wrote: > > > The range_cyclic writeback mode use the address_space > > > writeback_index as the start index for writeback. With > > > delayed allocation we were updating writeback_index > > > wrongly resulting in highly fragmented file. Number of > > > extents reduced from 4000 to 27 for a 3GB file with > > > the below patch. > > > > > > > I tested the ext4 patch queue from today on top of 2.6.27, and this > > includes Aneesh's latest patches. > > > > Things are going at disk speed for streaming writes, with the number of > > extents generated for a 32GB file down to 27. So, this is definitely an > > improvement for ext4. > > Just FYI, I ran this with compilebench -i 20 --makej and my log is full > of these: > > ext4_da_writepages: jbd2_start: 1024 pages, ino 520417; err -30 > Pid: 4072, comm: pdflush Not tainted 2.6.27 #2 > > Call Trace: > [] ext4_da_writepages+0x171/0x2d3 [ext4] > [] ? pick_next_task_fair+0x80/0x91 > [] ? source_load+0x2a/0x58 > [] ? __next_cpu+0x19/0x26 > [] do_writepages+0x28/0x37 > [] __writeback_single_inode+0x14f/0x26d > [] generic_sync_sb_inodes+0x1c1/0x2a2 > [] sync_sb_inodes+0x9/0xb > [] writeback_inodes+0x64/0xad > [] wb_kupdate+0x9a/0x10c > [] ? pdflush+0x0/0x1e9 > [] ? pdflush+0x0/0x1e9 > [] pdflush+0x13d/0x1e9 > [] ? wb_kupdate+0x0/0x10c > [] kthread+0x49/0x77 > [] child_rip+0xa/0x11 > [] ? kthread+0x0/0x77 > [] ? child_rip+0x0/0x11 I actually did the mount -o remount,ro test before sending out the patches to see if we are skipping some pages during writeback. I didn't see the error at that time. Today i tried again on a larger file system and i am able to reproduce the above stack with -o remount,ro. The patch below fix it for me. The VFS writeback looks at pages_skipped and make some decision if the value increase during call back(__fynsc_super -> generic_sync_sb_inodes). So we need to update pages_skipped also. This may not apply on top of what patches are in patchqueue. I also have other changes to use single variable no_nrwite_index_update as per Christoph suggestion. I will send out the patches for patchqueue after I look at the compile bench numbers you reported. diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 3c4b9b4..88ce29e 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2370,10 +2370,10 @@ static int ext4_da_writepages(struct address_space *mapping, pgoff_t index; int range_whole = 0; handle_t *handle = NULL; - long pages_written = 0; struct mpage_da_data mpd; struct inode *inode = mapping->host; int no_nrwrite_index_update; + long pages_written = 0, pages_skipped; int needed_blocks, ret = 0, nr_to_writebump = 0; struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb); @@ -2411,6 +2411,7 @@ static int ext4_da_writepages(struct address_space *mapping, */ no_nrwrite_index_update = wbc->no_nrwrite_index_update; wbc->no_nrwrite_index_update = 1; + pages_skipped = wbc->pages_skipped; while (!ret && wbc->nr_to_write > 0) { @@ -2444,6 +2445,7 @@ static int ext4_da_writepages(struct address_space *mapping, * and try again */ jbd2_journal_force_commit_nested(sbi->s_journal); + wbc->pages_skipped = pages_skipeed; ret = 0; } else if (ret == MPAGE_DA_EXTENT_TAIL) { /* @@ -2451,6 +2453,7 @@ static int ext4_da_writepages(struct address_space *mapping, * rest of the pages */ pages_written += mpd.pages_written; + wbc->pages_skipped = pages_skipeed; ret = 0; } else if (wbc->nr_to_write) /*