From: Eric Sandeen Subject: [PATCH] ext4: fix 50% disk write performance regression Date: Mon, 30 Aug 2010 22:43:46 -0500 Message-ID: <4C7C7A72.3020001@redhat.com> References: <20100829231126.8d8b2086.billfink@mindspring.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: tytso@mit.edu, adilger@sun.com, linux-ext4@vger.kernel.org, bill.fink@nasa.gov To: Bill Fink Return-path: Received: from mx1.redhat.com ([209.132.183.28]:35996 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932067Ab0HaDnz (ORCPT ); Mon, 30 Aug 2010 23:43:55 -0400 In-Reply-To: <20100829231126.8d8b2086.billfink@mindspring.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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 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,