Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758385AbYA1D3O (ORCPT ); Sun, 27 Jan 2008 22:29:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753516AbYA1D3E (ORCPT ); Sun, 27 Jan 2008 22:29:04 -0500 Received: from smtp.ustc.edu.cn ([202.38.64.16]:48352 "HELO ustc.edu.cn" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1750727AbYA1D3B (ORCPT ); Sun, 27 Jan 2008 22:29:01 -0500 Message-ID: <401490949.20091@ustc.edu.cn> X-EYOUMAIL-SMTPAUTH: wfg@mail.ustc.edu.cn Date: Mon, 28 Jan 2008 11:28:51 +0800 From: Fengguang Wu To: Andrew Morton Cc: linux-kernel@vger.kernel.org Subject: [PATCH] writeback: speed up writeback of big dirty files MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-GPG-Fingerprint: 53D2 DDCE AB5C 8DC6 188B 1CB1 F766 DA34 8D8B 1C6D User-Agent: Mutt/1.5.12-2006-07-14 Message-Id: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5102 Lines: 143 Andrew, I'd suggest it for 2.6.25. It's a safer version of the reverted patch in .24-rc8. It was tested on ext2/ext3/jfs/xfs/reiserfs and won't 100% iowait even without the other bug fixing patches. Fengguang --- writeback: speed up writeback of big dirty files After making dirty a 100M file, the normal behavior is to start the writeback for all data after 30s delays. But sometimes the following happens instead: - after 30s: ~4M - after 5s: ~4M - after 5s: all remaining 92M Some analyze shows that the internal io dispatch queues goes like this: s_io s_more_io ------------------------- 1) 100M,1K 0 2) 1K 96M 3) 0 96M 1) initial state with a 100M file and a 1K file 2) 4M written, nr_to_write <= 0, so write more 3) 1K written, nr_to_write > 0, no more writes(BUG) nr_to_write > 0 in (3) fools the upper layer to think that data have all been written out. The big dirty file is actually still sitting in s_more_io. We cannot simply splice s_more_io back to s_io as soon as s_io becomes empty, and let the loop in generic_sync_sb_inodes() continue: this may starve newly expired inodes in s_dirty. It is also not an option to draw inodes from both s_more_io and s_dirty, an let the loop go on: this might lead to live locks, and might also starve other superblocks in sync time(well kupdate may still starve some superblocks, that's another bug). We have to return when a full scan of s_io completes. So nr_to_write > 0 does not necessarily mean that "all data are written". This patch introduces a flag writeback_control.more_io to indicate that more io should be done. With it the big dirty file no longer has to wait for the next kupdate invocation 5s later. In sync_sb_inodes() we only set more_io on super_blocks we actually visited. This aviods the interaction between two pdflush deamons. Also in __sync_single_inode() we don't blindly keep requeuing the io if the filesystem cannot progress. Failing to do so may lead to 100% iowait. Tested-by: Mike Snitzer Signed-off-by: Fengguang Wu --- fs/fs-writeback.c | 18 ++++++++++++++++-- include/linux/writeback.h | 1 + mm/page-writeback.c | 9 ++++++--- 3 files changed, 23 insertions(+), 5 deletions(-) --- linux-mm.orig/fs/fs-writeback.c +++ linux-mm/fs/fs-writeback.c @@ -284,7 +284,17 @@ __sync_single_inode(struct inode *inode, * soon as the queue becomes uncongested. */ inode->i_state |= I_DIRTY_PAGES; - requeue_io(inode); + if (wbc->nr_to_write <= 0) { + /* + * slice used up: queue for next turn + */ + requeue_io(inode); + } else { + /* + * somehow blocked: retry later + */ + redirty_tail(inode); + } } else { /* * Otherwise fully redirty the inode so that @@ -468,8 +478,12 @@ void generic_sync_sb_inodes(struct super iput(inode); cond_resched(); spin_lock(&inode_lock); - if (wbc->nr_to_write <= 0) + if (wbc->nr_to_write <= 0) { + wbc->more_io = 1; break; + } + if (!list_empty(&sb->s_more_io)) + wbc->more_io = 1; } spin_unlock(&inode_lock); return; /* Leave any unwritten inodes on s_io */ --- linux-mm.orig/include/linux/writeback.h +++ linux-mm/include/linux/writeback.h @@ -62,6 +62,7 @@ struct writeback_control { unsigned for_reclaim:1; /* Invoked from the page allocator */ unsigned for_writepages:1; /* This is a writepages() call */ unsigned range_cyclic:1; /* range_start is cyclic */ + unsigned more_io:1; /* more io to be dispatched */ }; /* --- linux-mm.orig/mm/page-writeback.c +++ linux-mm/mm/page-writeback.c @@ -567,6 +567,7 @@ static void background_writeout(unsigned global_page_state(NR_UNSTABLE_NFS) < background_thresh && min_pages <= 0) break; + wbc.more_io = 0; wbc.encountered_congestion = 0; wbc.nr_to_write = MAX_WRITEBACK_PAGES; wbc.pages_skipped = 0; @@ -574,8 +575,9 @@ static void background_writeout(unsigned min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) { /* Wrote less than expected */ - congestion_wait(WRITE, HZ/10); - if (!wbc.encountered_congestion) + if (wbc.encountered_congestion || wbc.more_io) + congestion_wait(WRITE, HZ/10); + else break; } } @@ -640,11 +642,12 @@ static void wb_kupdate(unsigned long arg global_page_state(NR_UNSTABLE_NFS) + (inodes_stat.nr_inodes - inodes_stat.nr_unused); while (nr_to_write > 0) { + wbc.more_io = 0; wbc.encountered_congestion = 0; wbc.nr_to_write = MAX_WRITEBACK_PAGES; writeback_inodes(&wbc); if (wbc.nr_to_write > 0) { - if (wbc.encountered_congestion) + if (wbc.encountered_congestion || wbc.more_io) congestion_wait(WRITE, HZ/10); else break; /* All the old data is written */ -- 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/