On Mon, Sep 21, 2009 at 11:04:02AM +0800, Wu Fengguang wrote: > On Mon, Sep 21, 2009 at 03:00:06AM +0800, Jan Kara wrote: > > On Sat 19-09-09 23:03:51, Wu Fengguang wrote: > > > On Sat, Sep 19, 2009 at 12:26:07PM +0800, Wu Fengguang wrote: > > > > On Sat, Sep 19, 2009 at 12:00:51PM +0800, Wu Fengguang wrote: > > > > > On Sat, Sep 19, 2009 at 11:58:35AM +0800, Wu Fengguang wrote: > > > > > > On Sat, Sep 19, 2009 at 01:52:52AM +0800, Theodore Tso wrote: > > > > > > > On Fri, Sep 11, 2009 at 10:39:29PM +0800, Wu Fengguang wrote: > > > > > > > > > > > > > > > > That would be good. Sorry for the late work. I'll allocate some time > > > > > > > > in mid next week to help review and benchmark recent writeback works, > > > > > > > > and hope to get things done in this merge window. > > > > > > > > > > > > > > Did you have some chance to get more work done on the your writeback > > > > > > > patches? > > > > > > > > > > > > Sorry for the delay, I'm now testing the patches with commands > > > > > > > > > > > > cp /dev/zero /mnt/test/zero0 & > > > > > > dd if=/dev/zero of=/mnt/test/zero1 & > > > > > > > > > > > > and the attached debug patch. > > > > > > > > > > > > One problem I found with ext3/4 is, redirty_tail() is called repeatedly > > > > > > in the traces, which could slow down the inode writeback significantly. > > > > > > > > > > FYI, it's this redirty_tail() called in writeback_single_inode(): > > > > > > > > > > /* > > > > > * Someone redirtied the inode while were writing back > > > > > * the pages. > > > > > */ > > > > > redirty_tail(inode); > > > > > > > > Hmm, this looks like an old fashioned problem get blew up by the > > > > 128MB MAX_WRITEBACK_PAGES. > > > > > > > > The inode was redirtied by the busy cp/dd processes. Now it takes much > > > > more time to sync 128MB, so that a heavy dirtier can easily redirty > > > > the inode in that time window. > > > > > > > > One single invocation of redirty_tail() could hold up the writeback of > > > > current inode for up to 30 seconds. > > > > > > It seems that this patch helps. However I'm afraid it's too late to > > > risk merging such kind of patches now.. > > Fenguang, could we maybe write down how the logic should look like > > and then look at the code and modify it as needed to fit the logic? > > Because I couldn't find a compact description of the logic anywhere > > in the code. > > Good idea. It makes sense to write something down in Documentation/ > or embedded as code comments. > > > Here is how I'd imaging the writeout logic should work: > > We would have just two lists - b_dirty and b_more_io. Both would be > > ordered by dirtied_when. > > Andrew has a very good description for the dirty/io/more_io queues: > > http://lkml.org/lkml/2006/2/7/5 > > | So the protocol would be: > | > | s_io: contains expired and non-expired dirty inodes, with expired ones at > | the head. Unexpired ones (at least) are in time order. > | > | s_more_io: contains dirty expired inodes which haven't been fully written. > | Ordering doesn't matter (unless someone goes and changes > | dirty_expire_centisecs - but as long as we don't do anything really bad in > | response to this we'll be OK). > | > | s_dirty: contains expired and non-expired dirty inodes. The non-expired > | ones are in time-of-dirtying order. > > Since then s_io was changed to hold only _expired_ dirty inodes at the > beginning of a full scan. It serves as a bounded set of dirty inodes. > So that when finished a full scan of it, the writeback can go on to > the next superblock, and old dirty files' writeback won't be delayed > infinitely by poring in newly dirty files. > > It seems that the boundary could also be provided by some > older_than_this timestamp. So removal of b_io is possible > at least on this purpose. Yeah, this is a scratch patch to remove b_io, I see no obvious difficulties in doing so. Thanks, Fengguang --- fs/btrfs/extent_io.c | 2 - fs/fs-writeback.c | 65 +++++++++------------------------- include/linux/backing-dev.h | 2 - include/linux/writeback.h | 4 +- mm/backing-dev.c | 1 mm/page-writeback.c | 1 6 files changed, 21 insertions(+), 54 deletions(-) --- linux.orig/fs/fs-writeback.c 2009-09-21 13:12:56.000000000 +0800 +++ linux/fs/fs-writeback.c 2009-09-21 13:12:57.000000000 +0800 @@ -284,7 +284,7 @@ static void redirty_tail(struct inode *i } /* - * requeue inode for re-scanning after bdi->b_io list is exhausted. + * requeue inode for re-scanning. */ static void requeue_io(struct inode *inode) { @@ -317,32 +317,6 @@ static bool inode_dirtied_after(struct i return ret; } -/* - * Move expired dirty inodes from @delaying_queue to @dispatch_queue. - */ -static void move_expired_inodes(struct list_head *delaying_queue, - struct list_head *dispatch_queue, - unsigned long *older_than_this) -{ - while (!list_empty(delaying_queue)) { - struct inode *inode = list_entry(delaying_queue->prev, - struct inode, i_list); - if (older_than_this && - inode_dirtied_after(inode, *older_than_this)) - break; - list_move(&inode->i_list, dispatch_queue); - } -} - -/* - * Queue all expired dirty inodes for io, eldest first. - */ -static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this) -{ - list_splice_init(&wb->b_more_io, wb->b_io.prev); - move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this); -} - static int write_inode(struct inode *inode, int sync) { if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) @@ -399,7 +373,7 @@ writeback_single_inode(struct inode *ino * writeback can proceed with the other inodes on s_io. * * We'll have another go at writing back this inode when we - * completed a full scan of b_io. + * completed a full scan. */ if (!wait) { requeue_io(inode); @@ -540,11 +514,11 @@ static void writeback_inodes_wb(struct b spin_lock(&inode_lock); - if (!wbc->for_kupdate || list_empty(&wb->b_io)) - queue_io(wb, wbc->older_than_this); + if (list_empty(&wb->b_dirty)) + list_splice_init(&wb->b_more_io, &wb->b_dirty); - while (!list_empty(&wb->b_io)) { - struct inode *inode = list_entry(wb->b_io.prev, + while (!list_empty(&wb->b_dirty)) { + struct inode *inode = list_entry(wb->b_dirty.prev, struct inode, i_list); long pages_skipped; @@ -590,8 +564,12 @@ static void writeback_inodes_wb(struct b * Was this inode dirtied after sync_sb_inodes was called? * This keeps sync from extra jobs and livelock. */ - if (inode_dirtied_after(inode, start)) - break; + if (inode_dirtied_after(inode, wbc->older_than_this)) { + if (list_empty(&wb->b_more_io)) + break; + list_splice_init(&wb->b_more_io, wb->b_dirty.prev); + continue; + } if (pin_sb_for_writeback(wbc, inode)) { requeue_io(inode); @@ -623,7 +601,7 @@ static void writeback_inodes_wb(struct b } spin_unlock(&inode_lock); - /* Leave any unwritten inodes on b_io */ + /* Leave any unwritten inodes on b_dirty */ } void writeback_inodes_wbc(struct writeback_control *wbc) @@ -674,18 +652,18 @@ static long wb_writeback(struct bdi_writ .bdi = wb->bdi, .sb = args->sb, .sync_mode = args->sync_mode, - .older_than_this = NULL, .for_kupdate = args->for_kupdate, .range_cyclic = args->range_cyclic, }; unsigned long oldest_jif; long wrote = 0; - if (wbc.for_kupdate) { - wbc.older_than_this = &oldest_jif; - oldest_jif = jiffies - + if (wbc.for_kupdate) + wbc.older_than_this = jiffies - msecs_to_jiffies(dirty_expire_interval * 10); - } + else + wbc.older_than_this = jiffies; + if (!wbc.range_cyclic) { wbc.range_start = 0; wbc.range_end = LLONG_MAX; @@ -1004,7 +982,7 @@ void __mark_inode_dirty(struct inode *in goto out; /* - * If the inode was already on b_dirty/b_io/b_more_io, don't + * If the inode was already on b_dirty/b_more_io, don't * reposition it (that would break b_dirty time-ordering). */ if (!was_dirty) { @@ -1041,11 +1019,6 @@ EXPORT_SYMBOL(__mark_inode_dirty); * This function assumes that the blockdev superblock's inodes are backed by * a variety of queues, so all inodes are searched. For other superblocks, * assume that all inodes are backed by the same queue. - * - * The inodes to be written are parked on bdi->b_io. They are moved back onto - * bdi->b_dirty as they are selected for writing. This way, none can be missed - * on the writer throttling path, and we get decent balancing between many - * throttled threads: we don't want them all piling up on inode_sync_wait. */ static void wait_sb_inodes(struct super_block *sb) { --- linux.orig/fs/btrfs/extent_io.c 2009-09-21 13:12:24.000000000 +0800 +++ linux/fs/btrfs/extent_io.c 2009-09-21 13:12:57.000000000 +0800 @@ -2467,7 +2467,6 @@ int extent_write_full_page(struct extent struct writeback_control wbc_writepages = { .bdi = wbc->bdi, .sync_mode = wbc->sync_mode, - .older_than_this = NULL, .nr_to_write = 64, .range_start = page_offset(page) + PAGE_CACHE_SIZE, .range_end = (loff_t)-1, @@ -2501,7 +2500,6 @@ int extent_write_locked_range(struct ext struct writeback_control wbc_writepages = { .bdi = inode->i_mapping->backing_dev_info, .sync_mode = mode, - .older_than_this = NULL, .nr_to_write = nr_pages * 2, .range_start = start, .range_end = end + 1, --- linux.orig/include/linux/writeback.h 2009-09-21 13:12:24.000000000 +0800 +++ linux/include/linux/writeback.h 2009-09-21 13:12:57.000000000 +0800 @@ -32,8 +32,8 @@ struct writeback_control { struct super_block *sb; /* if !NULL, only write inodes from this super_block */ enum writeback_sync_modes sync_mode; - unsigned long *older_than_this; /* If !NULL, only write back inodes - older than this */ + unsigned long older_than_this; /* only write back inodes older than + this */ long nr_to_write; /* Write this many pages, and decrement this for each page written */ long pages_skipped; /* Pages which were not written */ --- linux.orig/mm/backing-dev.c 2009-09-21 13:12:24.000000000 +0800 +++ linux/mm/backing-dev.c 2009-09-21 13:12:57.000000000 +0800 @@ -333,7 +333,6 @@ static void bdi_flush_io(struct backing_ struct writeback_control wbc = { .bdi = bdi, .sync_mode = WB_SYNC_NONE, - .older_than_this = NULL, .range_cyclic = 1, .nr_to_write = 1024, }; --- linux.orig/mm/page-writeback.c 2009-09-21 13:12:56.000000000 +0800 +++ linux/mm/page-writeback.c 2009-09-21 13:12:57.000000000 +0800 @@ -492,7 +492,6 @@ static void balance_dirty_pages(struct a struct writeback_control wbc = { .bdi = bdi, .sync_mode = WB_SYNC_NONE, - .older_than_this = NULL, .nr_to_write = write_chunk, .range_cyclic = 1, }; --- linux.orig/include/linux/backing-dev.h 2009-09-21 13:12:24.000000000 +0800 +++ linux/include/linux/backing-dev.h 2009-09-21 13:12:57.000000000 +0800 @@ -53,7 +53,6 @@ struct bdi_writeback { struct task_struct *task; /* writeback task */ struct list_head b_dirty; /* dirty inodes */ - struct list_head b_io; /* parked for writeback */ struct list_head b_more_io; /* parked for more writeback */ }; @@ -111,7 +110,6 @@ extern struct list_head bdi_list; static inline int wb_has_dirty_io(struct bdi_writeback *wb) { return !list_empty(&wb->b_dirty) || - !list_empty(&wb->b_io) || !list_empty(&wb->b_more_io); } -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
