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Date: Wed, 8 Jul 2015 10:24:53 +0200
From: Jan Kara <jack@...e.cz>
To: Tejun Heo <tj@...nel.org>
Cc: Jan Kara <jack@...e.cz>, axboe@...nel.dk,
linux-kernel@...r.kernel.org, hch@...radead.org,
hannes@...xchg.org, linux-fsdevel@...r.kernel.org,
vgoyal@...hat.com, lizefan@...wei.com, cgroups@...r.kernel.org,
linux-mm@...ck.org, mhocko@...e.cz, clm@...com,
fengguang.wu@...el.com, david@...morbit.com, gthelen@...gle.com,
khlebnikov@...dex-team.ru
Subject: Re: [PATCH block/for-4.3] writeback: remove
wb_writeback_work->single_wait/done
On Fri 03-07-15 18:12:23, Tejun Heo wrote:
> Hello, Jan.
>
> So, something like the following. It depends on other changes so
> won't apply as-is. I'll repost it as part of a patchset once -rc1
> drops.
>
> Thanks!
>
> ------ 8< ------
> wb_writeback_work->single_wait/done are used for the wait mechanism
> for synchronous wb_work (wb_writeback_work) items which are issued
> when bdi_split_work_to_wbs() fails to allocate memory for asynchronous
> wb_work items; however, there's no reason to use a separate wait
> mechanism for this. bdi_split_work_to_wbs() can simply use on-stack
> fallback wb_work item and separate wb_completion to wait for it.
>
> This patch removes wb_work->single_wait/done and the related code and
> make bdi_split_work_to_wbs() use on-stack fallback wb_work and
> wb_completion instead.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Suggested-by: Jan Kara <jack@...e.cz>
Thanks! The patch looks good. You can add:
Reviewed-by: Jan Kara <jack@...e.com>
Honza
> ---
> fs/fs-writeback.c | 116 +++++++++++++-----------------------------------------
> 1 file changed, 30 insertions(+), 86 deletions(-)
>
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -53,8 +53,6 @@ struct wb_writeback_work {
> unsigned int for_background:1;
> unsigned int for_sync:1; /* sync(2) WB_SYNC_ALL writeback */
> unsigned int auto_free:1; /* free on completion */
> - unsigned int single_wait:1;
> - unsigned int single_done:1;
> enum wb_reason reason; /* why was writeback initiated? */
>
> struct list_head list; /* pending work list */
> @@ -181,11 +179,8 @@ static void wb_queue_work(struct bdi_wri
> trace_writeback_queue(wb->bdi, work);
>
> spin_lock_bh(&wb->work_lock);
> - if (!test_bit(WB_registered, &wb->state)) {
> - if (work->single_wait)
> - work->single_done = 1;
> + if (!test_bit(WB_registered, &wb->state))
> goto out_unlock;
> - }
> if (work->done)
> atomic_inc(&work->done->cnt);
> list_add_tail(&work->list, &wb->work_list);
> @@ -737,32 +732,6 @@ int inode_congested(struct inode *inode,
> EXPORT_SYMBOL_GPL(inode_congested);
>
> /**
> - * wb_wait_for_single_work - wait for completion of a single bdi_writeback_work
> - * @bdi: bdi the work item was issued to
> - * @work: work item to wait for
> - *
> - * Wait for the completion of @work which was issued to one of @bdi's
> - * bdi_writeback's. The caller must have set @work->single_wait before
> - * issuing it. This wait operates independently fo
> - * wb_wait_for_completion() and also disables automatic freeing of @work.
> - */
> -static void wb_wait_for_single_work(struct backing_dev_info *bdi,
> - struct wb_writeback_work *work)
> -{
> - if (WARN_ON_ONCE(!work->single_wait))
> - return;
> -
> - wait_event(bdi->wb_waitq, work->single_done);
> -
> - /*
> - * Paired with smp_wmb() in wb_do_writeback() and ensures that all
> - * modifications to @work prior to assertion of ->single_done is
> - * visible to the caller once this function returns.
> - */
> - smp_rmb();
> -}
> -
> -/**
> * wb_split_bdi_pages - split nr_pages to write according to bandwidth
> * @wb: target bdi_writeback to split @nr_pages to
> * @nr_pages: number of pages to write for the whole bdi
> @@ -791,38 +760,6 @@ static long wb_split_bdi_pages(struct bd
> }
>
> /**
> - * wb_clone_and_queue_work - clone a wb_writeback_work and issue it to a wb
> - * @wb: target bdi_writeback
> - * @base_work: source wb_writeback_work
> - *
> - * Try to make a clone of @base_work and issue it to @wb. If cloning
> - * succeeds, %true is returned; otherwise, @base_work is issued directly
> - * and %false is returned. In the latter case, the caller is required to
> - * wait for @base_work's completion using wb_wait_for_single_work().
> - *
> - * A clone is auto-freed on completion. @base_work never is.
> - */
> -static bool wb_clone_and_queue_work(struct bdi_writeback *wb,
> - struct wb_writeback_work *base_work)
> -{
> - struct wb_writeback_work *work;
> -
> - work = kmalloc(sizeof(*work), GFP_ATOMIC);
> - if (work) {
> - *work = *base_work;
> - work->auto_free = 1;
> - work->single_wait = 0;
> - } else {
> - work = base_work;
> - work->auto_free = 0;
> - work->single_wait = 1;
> - }
> - work->single_done = 0;
> - wb_queue_work(wb, work);
> - return work != base_work;
> -}
> -
> -/**
> * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
> * @bdi: target backing_dev_info
> * @base_work: wb_writeback_work to issue
> @@ -837,7 +774,6 @@ static void bdi_split_work_to_wbs(struct
> struct wb_writeback_work *base_work,
> bool skip_if_busy)
> {
> - long nr_pages = base_work->nr_pages;
> int next_memcg_id = 0;
> struct bdi_writeback *wb;
> struct wb_iter iter;
> @@ -849,17 +785,39 @@ static void bdi_split_work_to_wbs(struct
> restart:
> rcu_read_lock();
> bdi_for_each_wb(wb, bdi, &iter, next_memcg_id) {
> + DEFINE_WB_COMPLETION_ONSTACK(fallback_work_done);
> + struct wb_writeback_work fallback_work;
> + struct wb_writeback_work *work;
> + long nr_pages;
> +
> if (!wb_has_dirty_io(wb) ||
> (skip_if_busy && writeback_in_progress(wb)))
> continue;
>
> - base_work->nr_pages = wb_split_bdi_pages(wb, nr_pages);
> - if (!wb_clone_and_queue_work(wb, base_work)) {
> - next_memcg_id = wb->memcg_css->id + 1;
> - rcu_read_unlock();
> - wb_wait_for_single_work(bdi, base_work);
> - goto restart;
> + nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
> +
> + work = kmalloc(sizeof(*work), GFP_ATOMIC);
> + if (work) {
> + *work = *base_work;
> + work->nr_pages = nr_pages;
> + work->auto_free = 1;
> + wb_queue_work(wb, work);
> + continue;
> }
> +
> + /* alloc failed, execute synchronously using on-stack fallback */
> + work = &fallback_work;
> + *work = *base_work;
> + work->nr_pages = nr_pages;
> + work->auto_free = 0;
> + work->done = &fallback_work_done;
> +
> + wb_queue_work(wb, work);
> +
> + next_memcg_id = wb->memcg_css->id + 1;
> + rcu_read_unlock();
> + wb_wait_for_completion(bdi, &fallback_work_done);
> + goto restart;
> }
> rcu_read_unlock();
> }
> @@ -901,8 +859,6 @@ static void bdi_split_work_to_wbs(struct
> if (bdi_has_dirty_io(bdi) &&
> (!skip_if_busy || !writeback_in_progress(&bdi->wb))) {
> base_work->auto_free = 0;
> - base_work->single_wait = 0;
> - base_work->single_done = 0;
> wb_queue_work(&bdi->wb, base_work);
> }
> }
> @@ -1793,26 +1749,14 @@ static long wb_do_writeback(struct bdi_w
> set_bit(WB_writeback_running, &wb->state);
> while ((work = get_next_work_item(wb)) != NULL) {
> struct wb_completion *done = work->done;
> - bool need_wake_up = false;
>
> trace_writeback_exec(wb->bdi, work);
>
> wrote += wb_writeback(wb, work);
>
> - if (work->single_wait) {
> - WARN_ON_ONCE(work->auto_free);
> - /* paired w/ rmb in wb_wait_for_single_work() */
> - smp_wmb();
> - work->single_done = 1;
> - need_wake_up = true;
> - } else if (work->auto_free) {
> + if (work->auto_free)
> kfree(work);
> - }
> -
> if (done && atomic_dec_and_test(&done->cnt))
> - need_wake_up = true;
> -
> - if (need_wake_up)
> wake_up_all(&wb->bdi->wb_waitq);
> }
>
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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