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SubjectRe: [PATCH 4/6] writeback: dont redirty tail an inode with dirty pages
On Sun, Jul 11, 2010 at 10:07:00AM +0800, Wu Fengguang wrote:
> This avoids delaying writeback for an expired (XFS) inode with lots of
> dirty pages, but no active dirtier at the moment. Previously we only do
> that for the kupdate case.
>
> CC: Dave Chinner <david@fromorbit.com>
> CC: Christoph Hellwig <hch@infradead.org>
> Acked-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> ---
> fs/fs-writeback.c | 20 +++++++-------------
> 1 file changed, 7 insertions(+), 13 deletions(-)
>
> --- linux-next.orig/fs/fs-writeback.c 2010-07-11 08:53:44.000000000 +0800
> +++ linux-next/fs/fs-writeback.c 2010-07-11 08:57:35.000000000 +0800
> @@ -367,18 +367,7 @@ writeback_single_inode(struct inode *ino
> spin_lock(&inode_lock);
> inode->i_state &= ~I_SYNC;
> if (!(inode->i_state & I_FREEING)) {
> - if ((inode->i_state & I_DIRTY_PAGES) && wbc->for_kupdate) {
> - /*
> - * More pages get dirtied by a fast dirtier.
> - */
> - goto select_queue;
> - } else if (inode->i_state & I_DIRTY) {
> - /*
> - * At least XFS will redirty the inode during the
> - * writeback (delalloc) and on io completion (isize).
> - */
> - redirty_tail(inode);
> - } else if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
> + if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
> /*
> * We didn't write back all the pages. nfs_writepages()
> * sometimes bales out without doing anything. Redirty
> @@ -400,7 +389,6 @@ writeback_single_inode(struct inode *ino
> * soon as the queue becomes uncongested.
> */
> inode->i_state |= I_DIRTY_PAGES;
> -select_queue:
> if (wbc->nr_to_write <= 0) {
> /*
> * slice used up: queue for next turn
> @@ -423,6 +411,12 @@ select_queue:
> inode->i_state |= I_DIRTY_PAGES;
> redirty_tail(inode);
> }
> + } else if (inode->i_state & I_DIRTY) {
> + /*
> + * At least XFS will redirty the inode during the
> + * writeback (delalloc) and on io completion (isize).
> + */
> + redirty_tail(inode);

I'd drop the mention of XFS here - any filesystem that does delayed
allocation or unwritten extent conversion after Io completion will
cause this. Perhaps make the comment:

/*
* Filesystems can dirty the inode during writeback
* operations, such as delayed allocation during submission
* or metadata updates after data IO completion.
*/
Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com


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