From: Theodore Tso Subject: Re: [PATCH, RFC] vm: Add an tuning knob for vm.max_writeback_pages Date: Mon, 31 Aug 2009 17:03:37 -0400 Message-ID: <20090831210337.GG23535@mit.edu> References: <1251600858-21294-1-git-send-email-tytso@mit.edu> <20090830165229.GA5189@infradead.org> <20090830181731.GA20822@mit.edu> <20090830222710.GA9938@infradead.org> <20090831030815.GD20822@mit.edu> <20090831102909.GS12579@kernel.dk> <20090831104748.GT12579@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , linux-mm@kvack.org, Ext4 Developers List , linux-fsdevel@vger.kernel.org, chris.mason@oracle.com To: Jens Axboe Return-path: Content-Disposition: inline In-Reply-To: <20090831104748.GT12579@kernel.dk> Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org On Mon, Aug 31, 2009 at 12:47:49PM +0200, Jens Axboe wrote: > It's because ext4 writepages sets ->range_start and wb_writeback() is > range cyclic, then the next iteration will have the previous end point > as the starting point. Looks like we need to clear ->range_start in > wb_writeback(), the better place is probably to do that in > fs/fs-writeback.c:generic_sync_wb_inodes() right after the > writeback_single_inode() call. This, btw, should be no different than > the current code, weird/correct or not :-) Thanks for pointing it out. After staring at the code, I now believe this is the best fix for now. What do other folks think? - Ted commit 39cac8147479b48cd45b768d184aa6a80f23a2f7 Author: Theodore Ts'o Date: Mon Aug 31 17:00:59 2009 -0400 ext4: Restore wbc->range_start in ext4_da_writepages() To solve a lock inversion problem, we implement part of the range_cyclic algorithm in ext4_da_writepages(). (See commit 2acf2c26 for more details.) As part of that change wbc->range_start was modified by ext4's writepages function, which causes its callers to get confused since they aren't expecting the filesystem to modify it. The simplest fix is to save and restore wbc->range_start in ext4_da_writepages. Signed-off-by: "Theodore Ts'o" diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index d61fb52..ff659e7 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2749,6 +2749,7 @@ static int ext4_da_writepages(struct address_space *mapping, long pages_skipped; int range_cyclic, cycled = 1, io_done = 0; int needed_blocks, ret = 0, nr_to_writebump = 0; + loff_t range_start = wbc->range_start; struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb); trace_ext4_da_writepages(inode, wbc); @@ -2917,6 +2918,7 @@ out_writepages: if (!no_nrwrite_index_update) wbc->no_nrwrite_index_update = 0; wbc->nr_to_write -= nr_to_writebump; + wbc->range_start = range_start; trace_ext4_da_writepages_result(inode, wbc, ret, pages_written); return ret; } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org