Re: [PATCH 4/6] writeback: introduce writeback_control.inodes_cleaned

Jan Kara
2011-04-19T09:48:29Z

On Tue 19-04-11 11:00:07, Wu Fengguang wrote:
> The flusher works on dirty inodes in batches, and may quit prematurely
> if the batch of inodes happen to be metadata-only dirtied: in this case
> wbc->nr_to_write won't be decreased at all, which stands for "no pages
> written" but also mis-interpreted as "no progress".
>
> So introduce writeback_control.inodes_cleaned to count the inodes get
> cleaned. A non-zero value means there are some progress on writeback,
> in which case more writeback can be tried.
>
> about v1: The initial version was to count successful ->write_inode()
> calls. However it leads to busy loops for sync() over NFS, because NFS
> ridiculously returns 0 (success) while at the same time redirties the
> inode. The NFS case can be trivially fixed, however there may be more
> hidden bugs in other filesystems..
OK, makes sense.
Acked-by: Jan Kara <jack@suse.cz>

Honza
>
> Acked-by: Mel Gorman <mel@csn.ul.ie>
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> ---
> fs/fs-writeback.c | 4 ++++
> include/linux/writeback.h | 1 +
> 2 files changed, 5 insertions(+)
>
> --- linux-next.orig/fs/fs-writeback.c 2011-04-19 10:18:30.000000000 +0800
> +++ linux-next/fs/fs-writeback.c 2011-04-19 10:18:30.000000000 +0800
> @@ -473,6 +473,7 @@ writeback_single_inode(struct inode *ino
> * No need to add it back to the LRU.
> */
> list_del_init(&inode->i_wb_list);
> + wbc->inodes_cleaned++;
> }
> }
> inode_sync_complete(inode);
> @@ -736,6 +737,7 @@ static long wb_writeback(struct bdi_writ
> wbc.more_io = 0;
> wbc.nr_to_write = write_chunk;
> wbc.pages_skipped = 0;
> + wbc.inodes_cleaned = 0;
>
> trace_wbc_writeback_start(&wbc, wb->bdi);
> if (work->sb)
> @@ -752,6 +754,8 @@ static long wb_writeback(struct bdi_writ
> */
> if (wbc.nr_to_write <= 0)
> continue;
> + if (wbc.inodes_cleaned)
> + continue;
> /*
> * Didn't write everything and we don't have more IO, bail
> */
> --- linux-next.orig/include/linux/writeback.h 2011-04-19 10:18:17.000000000 +0800
> +++ linux-next/include/linux/writeback.h 2011-04-19 10:18:30.000000000 +0800
> @@ -34,6 +34,7 @@ struct writeback_control {
> long nr_to_write; /* Write this many pages, and decrement
> this for each page written */
> long pages_skipped; /* Pages which were not written */
> + long inodes_cleaned; /* # of inodes cleaned */
>
> /*
> * For a_ops->writepages(): is start or end are non-zero then this is
>
>
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR