Re: [PATCH 01/10] writeback: move backing_dev_info->state into bdi_writeback

From: Jan Kara
Date: Thu Nov 20 2014 - 10:27:20 EST

On Tue 18-11-14 03:37:19, Tejun Heo wrote:
> Currently, a bdi (backing_dev_info) embeds single wb (bdi_writeback)
> and the role of the separation is unclear. For cgroup support for
> writeback IOs, a bdi will be updated to host multiple wb's where each
> wb serves writeback IOs of a different cgroup on the bdi. To achieve
> that, a wb should carry all states necessary for servicing writeback
> IOs for a cgroup independently.
>
> This patch moves bdi->state into wb.
>
> * enum bdi_state is renamed to wb_state and the prefix of all enums is
> changed from BDI_ to WB_.
>
> * Explicit zeroing of bdi->state is removed without adding zeoring of
> wb->state as the whole data structure is zeroed on init anyway.
>
> * As there's still only one bdi_writeback per backing_dev_info, all
> uses of bdi->state are mechanically replaced with bdi->wb.state
> introducing no behavior changes.
Hum, does it make sense to convert BDI_sync_congested and
BDI_async_congested? It contains information whether the *device* is
congested and cannot take more work. I understand that in a cgroup world
you want to throttle IO from a cgroup to a device so when you take
bdi_writeback to be a per-cgroup structure you want some indication there
that a particular cgroup cannot push more to the device. But is it that
e.g. mdraid cares about a cgroup and not about the device?

Honza
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> Cc: drbd-dev@xxxxxxxxxxxxxxxx
> Cc: Neil Brown <neilb@xxxxxxx>
> Cc: Alasdair Kergon <agk@xxxxxxxxxx>
> Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> ---
> block/blk-core.c | 1 -
> drivers/block/drbd/drbd_main.c | 10 +++++-----
> drivers/md/dm.c | 2 +-
> drivers/md/raid1.c | 4 ++--
> drivers/md/raid10.c | 2 +-
> fs/fs-writeback.c | 14 +++++++-------
> include/linux/backing-dev.h | 24 ++++++++++++------------
> mm/backing-dev.c | 21 ++++++++++-----------
> 8 files changed, 38 insertions(+), 40 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 0421b53..8801682 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -584,7 +584,6 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
>
> q->backing_dev_info.ra_pages =
> (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
> - q->backing_dev_info.state = 0;
> q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
> q->backing_dev_info.name = "block";
> q->node = node_id;
> diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
> index 1fc8342..61b00aa 100644
> --- a/drivers/block/drbd/drbd_main.c
> +++ b/drivers/block/drbd/drbd_main.c
> @@ -2360,7 +2360,7 @@ static void drbd_cleanup(void)
> * @congested_data: User data
> * @bdi_bits: Bits the BDI flusher thread is currently interested in
> *
> - * Returns 1<<BDI_async_congested and/or 1<<BDI_sync_congested if we are congested.
> + * Returns 1<<WB_async_congested and/or 1<<WB_sync_congested if we are congested.
> */
> static int drbd_congested(void *congested_data, int bdi_bits)
> {
> @@ -2377,14 +2377,14 @@ static int drbd_congested(void *congested_data, int bdi_bits)
> }
>
> if (test_bit(CALLBACK_PENDING, &first_peer_device(device)->connection->flags)) {
> - r |= (1 << BDI_async_congested);
> + r |= (1 << WB_async_congested);
> /* Without good local data, we would need to read from remote,
> * and that would need the worker thread as well, which is
> * currently blocked waiting for that usermode helper to
> * finish.
> */
> if (!get_ldev_if_state(device, D_UP_TO_DATE))
> - r |= (1 << BDI_sync_congested);
> + r |= (1 << WB_sync_congested);
> else
> put_ldev(device);
> r &= bdi_bits;
> @@ -2400,9 +2400,9 @@ static int drbd_congested(void *congested_data, int bdi_bits)
> reason = 'b';
> }
>
> - if (bdi_bits & (1 << BDI_async_congested) &&
> + if (bdi_bits & (1 << WB_async_congested) &&
> test_bit(NET_CONGESTED, &first_peer_device(device)->connection->flags)) {
> - r |= (1 << BDI_async_congested);
> + r |= (1 << WB_async_congested);
> reason = reason == 'b' ? 'a' : 'n';
> }
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 58f3927..c4c53af 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1950,7 +1950,7 @@ static int dm_any_congested(void *congested_data, int bdi_bits)
> * the query about congestion status of request_queue
> */
> if (dm_request_based(md))
> - r = md->queue->backing_dev_info.state &
> + r = md->queue->backing_dev_info.wb.state &
> bdi_bits;
> else
> r = dm_table_any_congested(map, bdi_bits);
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 40b35be..aad1482 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -739,7 +739,7 @@ int md_raid1_congested(struct mddev *mddev, int bits)
> struct r1conf *conf = mddev->private;
> int i, ret = 0;
>
> - if ((bits & (1 << BDI_async_congested)) &&
> + if ((bits & (1 << WB_async_congested)) &&
> conf->pending_count >= max_queued_requests)
> return 1;
>
> @@ -754,7 +754,7 @@ int md_raid1_congested(struct mddev *mddev, int bits)
> /* Note the '|| 1' - when read_balance prefers
> * non-congested targets, it can be removed
> */
> - if ((bits & (1<<BDI_async_congested)) || 1)
> + if ((bits & (1<<WB_async_congested)) || 1)
> ret |= bdi_congested(&q->backing_dev_info, bits);
> else
> ret &= bdi_congested(&q->backing_dev_info, bits);
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 32e282f..5180e75 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -915,7 +915,7 @@ int md_raid10_congested(struct mddev *mddev, int bits)
> struct r10conf *conf = mddev->private;
> int i, ret = 0;
>
> - if ((bits & (1 << BDI_async_congested)) &&
> + if ((bits & (1 << WB_async_congested)) &&
> conf->pending_count >= max_queued_requests)
> return 1;
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 2d609a5..a797bda 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -62,7 +62,7 @@ struct wb_writeback_work {
> */
> int writeback_in_progress(struct backing_dev_info *bdi)
> {
> - return test_bit(BDI_writeback_running, &bdi->state);
> + return test_bit(WB_writeback_running, &bdi->wb.state);
> }
> EXPORT_SYMBOL(writeback_in_progress);
>
> @@ -94,7 +94,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
> static void bdi_wakeup_thread(struct backing_dev_info *bdi)
> {
> spin_lock_bh(&bdi->wb_lock);
> - if (test_bit(BDI_registered, &bdi->state))
> + if (test_bit(WB_registered, &bdi->wb.state))
> mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
> spin_unlock_bh(&bdi->wb_lock);
> }
> @@ -105,7 +105,7 @@ static void bdi_queue_work(struct backing_dev_info *bdi,
> trace_writeback_queue(bdi, work);
>
> spin_lock_bh(&bdi->wb_lock);
> - if (!test_bit(BDI_registered, &bdi->state)) {
> + if (!test_bit(WB_registered, &bdi->wb.state)) {
> if (work->done)
> complete(work->done);
> goto out_unlock;
> @@ -1007,7 +1007,7 @@ static long wb_do_writeback(struct bdi_writeback *wb)
> struct wb_writeback_work *work;
> long wrote = 0;
>
> - set_bit(BDI_writeback_running, &wb->bdi->state);
> + set_bit(WB_writeback_running, &wb->state);
> while ((work = get_next_work_item(bdi)) != NULL) {
>
> trace_writeback_exec(bdi, work);
> @@ -1029,7 +1029,7 @@ static long wb_do_writeback(struct bdi_writeback *wb)
> */
> wrote += wb_check_old_data_flush(wb);
> wrote += wb_check_background_flush(wb);
> - clear_bit(BDI_writeback_running, &wb->bdi->state);
> + clear_bit(WB_writeback_running, &wb->state);
>
> return wrote;
> }
> @@ -1049,7 +1049,7 @@ void bdi_writeback_workfn(struct work_struct *work)
> current->flags |= PF_SWAPWRITE;
>
> if (likely(!current_is_workqueue_rescuer() ||
> - !test_bit(BDI_registered, &bdi->state))) {
> + !test_bit(WB_registered, &wb->state))) {
> /*
> * The normal path. Keep writing back @bdi until its
> * work_list is empty. Note that this path is also taken
> @@ -1211,7 +1211,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
> spin_unlock(&inode->i_lock);
> spin_lock(&bdi->wb.list_lock);
> if (bdi_cap_writeback_dirty(bdi)) {
> - WARN(!test_bit(BDI_registered, &bdi->state),
> + WARN(!test_bit(WB_registered, &bdi->wb.state),
> "bdi-%s not registered\n", bdi->name);
>
> /*
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 5da6012..a356ccd 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -25,13 +25,13 @@ struct device;
> struct dentry;
>
> /*
> - * Bits in backing_dev_info.state
> + * Bits in bdi_writeback.state
> */
> -enum bdi_state {
> - BDI_async_congested, /* The async (write) queue is getting full */
> - BDI_sync_congested, /* The sync queue is getting full */
> - BDI_registered, /* bdi_register() was done */
> - BDI_writeback_running, /* Writeback is in progress */
> +enum wb_state {
> + WB_async_congested, /* The async (write) queue is getting full */
> + WB_sync_congested, /* The sync queue is getting full */
> + WB_registered, /* bdi_register() was done */
> + WB_writeback_running, /* Writeback is in progress */
> };
>
> typedef int (congested_fn)(void *, int);
> @@ -49,6 +49,7 @@ enum bdi_stat_item {
> struct bdi_writeback {
> struct backing_dev_info *bdi; /* our parent bdi */
>
> + unsigned long state; /* Always use atomic bitops on this */
> unsigned long last_old_flush; /* last old data flush */
>
> struct delayed_work dwork; /* work item used for writeback */
> @@ -61,7 +62,6 @@ struct bdi_writeback {
> struct backing_dev_info {
> struct list_head bdi_list;
> unsigned long ra_pages; /* max readahead in PAGE_CACHE_SIZE units */
> - unsigned long state; /* Always use atomic bitops on this */
> unsigned int capabilities; /* Device capabilities */
> congested_fn *congested_fn; /* Function pointer if device is md/dm */
> void *congested_data; /* Pointer to aux data for congested func */
> @@ -276,23 +276,23 @@ static inline int bdi_congested(struct backing_dev_info *bdi, int bdi_bits)
> {
> if (bdi->congested_fn)
> return bdi->congested_fn(bdi->congested_data, bdi_bits);
> - return (bdi->state & bdi_bits);
> + return (bdi->wb.state & bdi_bits);
> }
>
> static inline int bdi_read_congested(struct backing_dev_info *bdi)
> {
> - return bdi_congested(bdi, 1 << BDI_sync_congested);
> + return bdi_congested(bdi, 1 << WB_sync_congested);
> }
>
> static inline int bdi_write_congested(struct backing_dev_info *bdi)
> {
> - return bdi_congested(bdi, 1 << BDI_async_congested);
> + return bdi_congested(bdi, 1 << WB_async_congested);
> }
>
> static inline int bdi_rw_congested(struct backing_dev_info *bdi)
> {
> - return bdi_congested(bdi, (1 << BDI_sync_congested) |
> - (1 << BDI_async_congested));
> + return bdi_congested(bdi, (1 << WB_sync_congested) |
> + (1 << WB_async_congested));
> }
>
> enum {
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index 0ae0df5..62f3b33 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -17,7 +17,6 @@ static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
> struct backing_dev_info default_backing_dev_info = {
> .name = "default",
> .ra_pages = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
> - .state = 0,
> .capabilities = BDI_CAP_MAP_COPY,
> };
> EXPORT_SYMBOL_GPL(default_backing_dev_info);
> @@ -111,7 +110,7 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
> nr_dirty,
> nr_io,
> nr_more_io,
> - !list_empty(&bdi->bdi_list), bdi->state);
> + !list_empty(&bdi->bdi_list), bdi->wb.state);
> #undef K
>
> return 0;
> @@ -298,7 +297,7 @@ void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
>
> timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
> spin_lock_bh(&bdi->wb_lock);
> - if (test_bit(BDI_registered, &bdi->state))
> + if (test_bit(WB_registered, &bdi->wb.state))
> queue_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
> spin_unlock_bh(&bdi->wb_lock);
> }
> @@ -333,7 +332,7 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
> bdi->dev = dev;
>
> bdi_debug_register(bdi, dev_name(dev));
> - set_bit(BDI_registered, &bdi->state);
> + set_bit(WB_registered, &bdi->wb.state);
>
> spin_lock_bh(&bdi_lock);
> list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
> @@ -365,7 +364,7 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
>
> /* Make sure nobody queues further work */
> spin_lock_bh(&bdi->wb_lock);
> - clear_bit(BDI_registered, &bdi->state);
> + clear_bit(WB_registered, &bdi->wb.state);
> spin_unlock_bh(&bdi->wb_lock);
>
> /*
> @@ -543,11 +542,11 @@ static atomic_t nr_bdi_congested[2];
>
> void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
> {
> - enum bdi_state bit;
> + enum wb_state bit;
> wait_queue_head_t *wqh = &congestion_wqh[sync];
>
> - bit = sync ? BDI_sync_congested : BDI_async_congested;
> - if (test_and_clear_bit(bit, &bdi->state))
> + bit = sync ? WB_sync_congested : WB_async_congested;
> + if (test_and_clear_bit(bit, &bdi->wb.state))
> atomic_dec(&nr_bdi_congested[sync]);
> smp_mb__after_atomic();
> if (waitqueue_active(wqh))
> @@ -557,10 +556,10 @@ EXPORT_SYMBOL(clear_bdi_congested);
>
> void set_bdi_congested(struct backing_dev_info *bdi, int sync)
> {
> - enum bdi_state bit;
> + enum wb_state bit;
>
> - bit = sync ? BDI_sync_congested : BDI_async_congested;
> - if (!test_and_set_bit(bit, &bdi->state))
> + bit = sync ? WB_sync_congested : WB_async_congested;
> + if (!test_and_set_bit(bit, &bdi->wb.state))
> atomic_inc(&nr_bdi_congested[sync]);
> }
> EXPORT_SYMBOL(set_bdi_congested);
> --
> 1.9.3
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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