On Thu 20-10-11 23:22:41, Wu Fengguang wrote:
> The problem is, redirty_tail() may update i_dirtied_when and result in
> 30s max delay. If redirty_tail() is called often enough, some inode may
> even be delayed for ever.
>
> So introduce the b_more_io_wait queue to park inodes that for some
> reason cannot be synced immediately. The inodes will be sent to b_io at
> the next b_io refill time, however won't be busy retried as b_more_io:
> when the redirtied inodes are all in b_more_io_wait, wb_writeback() will
> see empty b_more_io and hence break out of the loop.
>
> This would be the new data flow after converting all redirty_tail()
> calls to requeue_io_wait():
>
> b_dirty --> b_io --> b_more_io/b_more_io_wait --+
> ^ |
> | |
> +----------------------------------+
>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Dave Chinner <david@xxxxxxxxxxxxx>
> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
You can add:
Acked-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> fs/fs-writeback.c | 16 ++++++++++++++++
> include/linux/backing-dev.h | 8 +++++---
> mm/backing-dev.c | 10 ++++++++--
> 3 files changed, 29 insertions(+), 5 deletions(-)
>
> --- linux-next.orig/fs/fs-writeback.c 2011-10-20 23:13:48.000000000 +0800
> +++ linux-next/fs/fs-writeback.c 2011-10-20 23:19:12.000000000 +0800
> @@ -234,6 +234,21 @@ static void requeue_io(struct inode *ino
> list_move(&inode->i_wb_list, &wb->b_more_io);
> }
>
> +/*
> + * The inode should be retried in an opportunistic way.
> + *
> + * The only difference between b_more_io and b_more_io_wait is:
> + * wb_writeback() won't quit as long as b_more_io is not empty. When
> + * wb_writeback() quit on empty b_more_io and non-empty b_more_io_wait,
> + * the kupdate work will wakeup more frequently to retry the inodes in
> + * b_more_io_wait.
> + */
> +static void requeue_io_wait(struct inode *inode, struct bdi_writeback *wb)
> +{
> + assert_spin_locked(&wb->list_lock);
> + list_move(&inode->i_wb_list, &wb->b_more_io_wait);
> +}
> +
> static void inode_sync_complete(struct inode *inode)
> {
> /*
> @@ -321,6 +336,7 @@ static void queue_io(struct bdi_writebac
> int moved;
> assert_spin_locked(&wb->list_lock);
> list_splice_init(&wb->b_more_io, &wb->b_io);
> + list_splice_init(&wb->b_more_io_wait, &wb->b_io);
> moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
> trace_writeback_queue_io(wb, work, moved);
> }
> --- linux-next.orig/include/linux/backing-dev.h 2011-10-20 23:13:48.000000000 +0800
> +++ linux-next/include/linux/backing-dev.h 2011-10-20 23:13:50.000000000 +0800
> @@ -59,6 +59,7 @@ struct bdi_writeback {
> 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 */
> + struct list_head b_more_io_wait;/* opportunistic retry io */
> spinlock_t list_lock; /* protects the b_* lists */
> };
>
> @@ -133,9 +134,10 @@ extern struct list_head bdi_pending_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);
> + return !list_empty(&wb->b_dirty) ||
> + !list_empty(&wb->b_io) ||
> + !list_empty(&wb->b_more_io) ||
> + !list_empty(&wb->b_more_io_wait);
> }
>
> static inline void __add_bdi_stat(struct backing_dev_info *bdi,
> --- linux-next.orig/mm/backing-dev.c 2011-10-20 23:13:48.000000000 +0800
> +++ linux-next/mm/backing-dev.c 2011-10-20 23:13:50.000000000 +0800
> @@ -74,10 +74,10 @@ static int bdi_debug_stats_show(struct s
> unsigned long background_thresh;
> unsigned long dirty_thresh;
> unsigned long bdi_thresh;
> - unsigned long nr_dirty, nr_io, nr_more_io;
> + unsigned long nr_dirty, nr_io, nr_more_io, nr_more_io_wait;
> struct inode *inode;
>
> - nr_dirty = nr_io = nr_more_io = 0;
> + nr_dirty = nr_io = nr_more_io = nr_more_io_wait = 0;
> spin_lock(&wb->list_lock);
> list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
> nr_dirty++;
> @@ -85,6 +85,8 @@ static int bdi_debug_stats_show(struct s
> nr_io++;
> list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
> nr_more_io++;
> + list_for_each_entry(inode, &wb->b_more_io_wait, i_wb_list)
> + nr_more_io_wait++;
> spin_unlock(&wb->list_lock);
>
> global_dirty_limits(&background_thresh, &dirty_thresh);
> @@ -103,6 +105,7 @@ static int bdi_debug_stats_show(struct s
> "b_dirty: %10lu\n"
> "b_io: %10lu\n"
> "b_more_io: %10lu\n"
> + "b_more_io_wait: %10lu\n"
> "bdi_list: %10u\n"
> "state: %10lx\n",
> (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
> @@ -116,6 +119,7 @@ static int bdi_debug_stats_show(struct s
> nr_dirty,
> nr_io,
> nr_more_io,
> + nr_more_io_wait,
> !list_empty(&bdi->bdi_list), bdi->state);
> #undef K
>
> @@ -651,6 +655,7 @@ static void bdi_wb_init(struct bdi_write
> INIT_LIST_HEAD(&wb->b_dirty);
> INIT_LIST_HEAD(&wb->b_io);
> INIT_LIST_HEAD(&wb->b_more_io);
> + INIT_LIST_HEAD(&wb->b_more_io_wait);
> spin_lock_init(&wb->list_lock);
> setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
> }
> @@ -718,6 +723,7 @@ void bdi_destroy(struct backing_dev_info
> list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
> list_splice(&bdi->wb.b_io, &dst->b_io);
> list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
> + list_splice(&bdi->wb.b_more_io_wait, &dst->b_more_io_wait);
> spin_unlock(&bdi->wb.list_lock);
> spin_unlock(&dst->list_lock);
> }
>
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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