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writeback: fix writeback completion notifications

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The code dealing with bdi_work->state and completion of a bdi_work is a
major mess currently.  This patch makes sure we directly use one set of
flags to deal with it, and use it consistently, which means:

 - always notify about completion from the rcu callback.  We only ever
   wait for it from on-stack callers, so this simplification does not
   even cause a theoretical slowdown currently.  It also makes sure we
   don't miss out on the notification if we ever add other callers to
   wait for it.
 - make earlier completion notification depending on the on-stack
   allocation, not the sync mode.  If we introduce new callers that
   want to do WB_SYNC_NONE writeback from on-stack callers this will
   be nessecary.

Also rename bdi_wait_on_work_clear to bdi_wait_on_work_done and inline
a few small functions into their only caller to make the code
understandable.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Christoph Hellwig 2010-06-08 18:14:34 +02:00 committed by Jens Axboe
parent 7908a9e5fc
commit 7f0e7bed93
1 changed files with 15 additions and 50 deletions
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65
fs/fs-writeback.c
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@ -63,24 +63,16 @@ struct bdi_work {
};
enum {
WS_USED_B = 0,
WS_ONSTACK_B,
WS_INPROGRESS = 0,
WS_ONSTACK,
};
#define WS_USED (1 << WS_USED_B)
#define WS_ONSTACK (1 << WS_ONSTACK_B)
static inline bool bdi_work_on_stack(struct bdi_work *work)
{
return test_bit(WS_ONSTACK_B, &work->state);
}
static inline void bdi_work_init(struct bdi_work *work,
struct wb_writeback_args *args)
{
INIT_RCU_HEAD(&work->rcu_head);
work->args = *args;
work->state = WS_USED;
__set_bit(WS_INPROGRESS, &work->state);
}
/**
@ -95,43 +87,16 @@ int writeback_in_progress(struct backing_dev_info *bdi)
return !list_empty(&bdi->work_list);
}
static void bdi_work_clear(struct bdi_work *work)
{
clear_bit(WS_USED_B, &work->state);
smp_mb__after_clear_bit();
/*
* work can have disappeared at this point. bit waitq functions
* should be able to tolerate this, provided bdi_sched_wait does
* not dereference it's pointer argument.
*/
wake_up_bit(&work->state, WS_USED_B);
}
static void bdi_work_free(struct rcu_head *head)
{
struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);
if (!bdi_work_on_stack(work))
clear_bit(WS_INPROGRESS, &work->state);
smp_mb__after_clear_bit();
wake_up_bit(&work->state, WS_INPROGRESS);
if (!test_bit(WS_ONSTACK, &work->state))
kfree(work);
else
bdi_work_clear(work);
}
static void wb_work_complete(struct bdi_work *work)
{
const enum writeback_sync_modes sync_mode = work->args.sync_mode;
int onstack = bdi_work_on_stack(work);
/*
* For allocated work, we can clear the done/seen bit right here.
* For on-stack work, we need to postpone both the clear and free
* to after the RCU grace period, since the stack could be invalidated
* as soon as bdi_work_clear() has done the wakeup.
*/
if (!onstack)
bdi_work_clear(work);
if (sync_mode == WB_SYNC_NONE || onstack)
call_rcu(&work->rcu_head, bdi_work_free);
}
static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
@ -147,7 +112,7 @@ static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
list_del_rcu(&work->list);
spin_unlock(&bdi->wb_lock);
wb_work_complete(work);
call_rcu(&work->rcu_head, bdi_work_free);
}
}
@ -185,9 +150,9 @@ static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
* Used for on-stack allocated work items. The caller needs to wait until
* the wb threads have acked the work before it's safe to continue.
*/
static void bdi_wait_on_work_clear(struct bdi_work *work)
static void bdi_wait_on_work_done(struct bdi_work *work)
{
wait_on_bit(&work->state, WS_USED_B, bdi_sched_wait,
wait_on_bit(&work->state, WS_INPROGRESS, bdi_sched_wait,
TASK_UNINTERRUPTIBLE);
}
@ -234,10 +199,10 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi,
struct bdi_work work;
bdi_work_init(&work, &args);
work.state |= WS_ONSTACK;
__set_bit(WS_ONSTACK, &work.state);
bdi_queue_work(bdi, &work);
bdi_wait_on_work_clear(&work);
bdi_wait_on_work_done(&work);
}
/**
@ -911,7 +876,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
* If this isn't a data integrity operation, just notify
* that we have seen this work and we are now starting it.
*/
if (args.sync_mode == WB_SYNC_NONE)
if (!test_bit(WS_ONSTACK, &work->state))
wb_clear_pending(wb, work);
wrote += wb_writeback(wb, &args);
@ -920,7 +885,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
* This is a data integrity writeback, so only do the
* notification when we have completed the work.
*/
if (args.sync_mode == WB_SYNC_ALL)
if (test_bit(WS_ONSTACK, &work->state))
wb_clear_pending(wb, work);
}