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SubjectRe: [PATCH 1/7] writeback: merely wakeup flusher thread if work allocation fails for WB_SYNC_NONE
On Mon 14-09-09 11:36:28, Jens Axboe wrote:
> From: Christoph Hellwig <hch@infradead.org>
>
> Since it's an opportunistic writeback and not a data integrity action,
> don't punt to blocking writeback. Just wakeup the thread and it will
> flush old data.
>
> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Looks good. Acked-by: Jan Kara <jack@suse.cz>
BTW, don't we miss Christoph's Signed-off-by?

Honza

> ---
> fs/fs-writeback.c | 46 ++++++++++++++--------------------------------
> 1 files changed, 14 insertions(+), 32 deletions(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index da86ef5..1873fd0 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -75,13 +75,6 @@ static inline void bdi_work_init(struct bdi_work *work,
> work->state = WS_USED;
> }
>
> -static inline void bdi_work_init_on_stack(struct bdi_work *work,
> - struct writeback_control *wbc)
> -{
> - bdi_work_init(work, wbc);
> - work->state |= WS_ONSTACK;
> -}
> -
> /**
> * writeback_in_progress - determine whether there is writeback in progress
> * @bdi: the device's backing_dev_info structure.
> @@ -207,34 +200,23 @@ static struct bdi_work *bdi_alloc_work(struct writeback_control *wbc)
>
> void bdi_start_writeback(struct writeback_control *wbc)
> {
> - const bool must_wait = wbc->sync_mode == WB_SYNC_ALL;
> - struct bdi_work work_stack, *work = NULL;
> -
> - if (!must_wait)
> - work = bdi_alloc_work(wbc);
> + /*
> + * WB_SYNC_NONE is opportunistic writeback. If this allocation fails,
> + * bdi_queue_work() will wake up the thread and flush old data. This
> + * should ensure some amount of progress in freeing memory.
> + */
> + if (wbc->sync_mode != WB_SYNC_ALL) {
> + struct bdi_work *w = bdi_alloc_work(wbc);
>
> - if (!work) {
> - work = &work_stack;
> - bdi_work_init_on_stack(work, wbc);
> - }
> + bdi_queue_work(wbc->bdi, w);
> + } else {
> + struct bdi_work work;
>
> - bdi_queue_work(wbc->bdi, work);
> + bdi_work_init(&work, wbc);
> + work.state |= WS_ONSTACK;
>
> - /*
> - * If the sync mode is WB_SYNC_ALL, block waiting for the work to
> - * complete. If not, we only need to wait for the work to be started,
> - * if we allocated it on-stack. We use the same mechanism, if the
> - * wait bit is set in the bdi_work struct, then threads will not
> - * clear pending until after they are done.
> - *
> - * Note that work == &work_stack if must_wait is true, so we don't
> - * need to do call_rcu() here ever, since the completion path will
> - * have done that for us.
> - */
> - if (must_wait || work == &work_stack) {
> - bdi_wait_on_work_clear(work);
> - if (work != &work_stack)
> - call_rcu(&work->rcu_head, bdi_work_free);
> + bdi_queue_work(wbc->bdi, &work);
> + bdi_wait_on_work_clear(&work);
> }
> }
>
> --
> 1.6.4.1.207.g68ea
>
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR


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