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SubjectRe: [PATCH 2/6] writeback: the kupdate expire timestamp should be a moving target
On Thu, Jul 22, 2010 at 01:09:30PM +0800, Wu Fengguang wrote:
> Dynamicly compute the dirty expire timestamp at queue_io() time.
> Also remove writeback_control.older_than_this which is no longer used.
>
> writeback_control.older_than_this used to be determined at entrance to
> the kupdate writeback work. This _static_ timestamp may go stale if the
> kupdate work runs on and on. The flusher may then stuck with some old
> busy inodes, never considering newly expired inodes thereafter.
>
> This has two possible problems:
>
> - It is unfair for a large dirty inode to delay (for a long time) the
> writeback of small dirty inodes.
>
> - As time goes by, the large and busy dirty inode may contain only
> _freshly_ dirtied pages. Ignoring newly expired dirty inodes risks
> delaying the expired dirty pages to the end of LRU lists, triggering
> the very bad pageout(). Neverthless this patch merely addresses part
> of the problem.
>
> CC: Jan Kara <jack@suse.cz>
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> ---
> fs/fs-writeback.c | 24 +++++++++---------------
> include/linux/writeback.h | 2 --
> include/trace/events/writeback.h | 6 +-----
> mm/backing-dev.c | 1 -
> mm/page-writeback.c | 1 -
> 5 files changed, 10 insertions(+), 24 deletions(-)
>
> --- linux-next.orig/fs/fs-writeback.c 2010-07-21 22:20:01.000000000 +0800
> +++ linux-next/fs/fs-writeback.c 2010-07-22 11:23:27.000000000 +0800
> @@ -216,16 +216,23 @@ static void move_expired_inodes(struct l
> struct list_head *dispatch_queue,
> struct writeback_control *wbc)
> {
> + unsigned long expire_interval = 0;
> + unsigned long older_than_this;
> LIST_HEAD(tmp);
> struct list_head *pos, *node;
> struct super_block *sb = NULL;
> struct inode *inode;
> int do_sb_sort = 0;
>
> + if (wbc->for_kupdate) {
> + expire_interval = msecs_to_jiffies(dirty_expire_interval * 10);
> + older_than_this = jiffies - expire_interval;
> + }
> +
> while (!list_empty(delaying_queue)) {
> inode = list_entry(delaying_queue->prev, struct inode, i_list);
> - if (wbc->older_than_this &&
> - inode_dirtied_after(inode, *wbc->older_than_this))
> + if (expire_interval &&
> + inode_dirtied_after(inode, older_than_this))
> break;
> if (sb && sb != inode->i_sb)
> do_sb_sort = 1;
> @@ -583,29 +590,19 @@ static inline bool over_bground_thresh(v
> * Try to run once per dirty_writeback_interval. But if a writeback event
> * takes longer than a dirty_writeback_interval interval, then leave a
> * one-second gap.
> - *
> - * older_than_this takes precedence over nr_to_write. So we'll only write back
> - * all dirty pages if they are all attached to "old" mappings.
> */
> static long wb_writeback(struct bdi_writeback *wb,
> struct wb_writeback_work *work)
> {
> struct writeback_control wbc = {
> .sync_mode = work->sync_mode,
> - .older_than_this = NULL,
> .for_kupdate = work->for_kupdate,
> .for_background = work->for_background,
> .range_cyclic = work->range_cyclic,
> };
> - unsigned long oldest_jif;
> long wrote = 0;
> struct inode *inode;
>
> - if (wbc.for_kupdate) {
> - wbc.older_than_this = &oldest_jif;
> - oldest_jif = jiffies -
> - msecs_to_jiffies(dirty_expire_interval * 10);
> - }
> if (!wbc.range_cyclic) {
> wbc.range_start = 0;
> wbc.range_end = LLONG_MAX;
> @@ -998,9 +995,6 @@ EXPORT_SYMBOL(__mark_inode_dirty);
> * Write out a superblock's list of dirty inodes. A wait will be performed
> * upon no inodes, all inodes or the final one, depending upon sync_mode.
> *
> - * If older_than_this is non-NULL, then only write out inodes which
> - * had their first dirtying at a time earlier than *older_than_this.
> - *
> * If `bdi' is non-zero then we're being asked to writeback a specific queue.
> * This function assumes that the blockdev superblock's inodes are backed by
> * a variety of queues, so all inodes are searched. For other superblocks,
> --- linux-next.orig/include/linux/writeback.h 2010-07-21 22:20:02.000000000 +0800
> +++ linux-next/include/linux/writeback.h 2010-07-22 11:23:27.000000000 +0800
> @@ -28,8 +28,6 @@ enum writeback_sync_modes {
> */
> struct writeback_control {
> enum writeback_sync_modes sync_mode;
> - unsigned long *older_than_this; /* If !NULL, only write back inodes
> - older than this */
> unsigned long wb_start; /* Time writeback_inodes_wb was
> called. This is needed to avoid
> extra jobs and livelock */

In addtion, We shuld remove older_than_this in btrfs and reiser4.

--
Kind regards,
Minchan Kim


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