From: Bill Fink Subject: Re: [PATCH] ext4: fix 50% disk write performance regression Date: Tue, 31 Aug 2010 00:53:09 -0400 Message-ID: <20100831005309.2457743d.billfink@mindspring.com> References: <20100829231126.8d8b2086.billfink@mindspring.com> <4C7C7A72.3020001@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: tytso@mit.edu, adilger@sun.com, linux-ext4@vger.kernel.org, bill.fink@nasa.gov To: Eric Sandeen Return-path: Received: from elasmtp-galgo.atl.sa.earthlink.net ([209.86.89.61]:47204 "EHLO elasmtp-galgo.atl.sa.earthlink.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754479Ab0HaExy (ORCPT ); Tue, 31 Aug 2010 00:53:54 -0400 In-Reply-To: <4C7C7A72.3020001@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, 30 Aug 2010, Eric Sandeen wrote: > Can you give this a shot? > > The first hunk is, I think, the biggest problem. Even if > we get the max number of pages we need, we keep scanning forward > until "done" without doing any more actual, useful work. > > The 2nd hunk is an oddity, some places assign nr_to_write > to LONG_MAX, and we get here and multiply -that- by 8... giving > us "-8" for nr_to_write, that can't help things when we > do later comparisons on that number... > > I also see us asking to find pages starting at "idx" and > the first dirty page we find is well ahead of that, > I'm not sure if that's indicative of a problem or not. > > Anyway, want to give this a shot, in place of the patch you sent, > and see how it fares compared to stock and/or with your patch? > > It's build-and-sanity tested but not really performance tested here. > > Thanks, > -Eric Great! It looks like that does the trick. 2.6.35 + your patch: i7test7% dd if=/dev/zero of=/i7raid/bill/testfile1 bs=1M count=32768 32768+0 records in 32768+0 records out 34359738368 bytes (34 GB) copied, 50.6702 s, 678 MB/s That's the same performance as with my patch, and pretty darn close to the original 2.6.31 performance. -Thanks a bunch -Bill > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > index 4b8debe..33c2167 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -1207,8 +1207,10 @@ static pgoff_t ext4_num_dirty_pages(struct inode *inode, pgoff_t idx, > break; > idx++; > num++; > - if (num >= max_pages) > - break; > + if (num >= max_pages) { > + pagevec_release(&pvec); > + return num; > + } > } > pagevec_release(&pvec); > } > @@ -3002,7 +3004,7 @@ static int ext4_da_writepages(struct address_space *mapping, > * sbi->max_writeback_mb_bump whichever is smaller. > */ > max_pages = sbi->s_max_writeback_mb_bump << (20 - PAGE_CACHE_SHIFT); > - if (!range_cyclic && range_whole) > + if (!range_cyclic && range_whole && wbc->nr_to_write != LONG_MAX) > desired_nr_to_write = wbc->nr_to_write * 8; > else > desired_nr_to_write = ext4_num_dirty_pages(inode, index,