[PATCH 1/7] writeback: merely wakeup flusher thread if work allocation fails for WB_SYNC_NONE

Jens Axboe
2009-09-14T09:36:43Z

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>
---
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