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Subject[PATCH 06/10] writeback: allow sleepy exit of default writeback task
Date
Since we do lazy create of default writeback tasks for a bdi, we can
allow sleepy exit if it has been completely idle for 5 minutes.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
fs/fs-writeback.c | 30 +++++++++++++++++++++++++-----
include/linux/backing-dev.h | 5 +++++
include/linux/writeback.h | 2 +-
3 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 0423880..7e139d5 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -373,7 +373,7 @@ static struct bdi_work *get_next_work_item(struct backing_dev_info *bdi,
/*
* Retrieve work items and do the writeback they describe
*/
-void wb_do_writeback(struct bdi_writeback *wb, int force_wait)
+long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
{
struct backing_dev_info *bdi = wb->bdi;
struct bdi_work *work;
@@ -417,8 +417,10 @@ void wb_do_writeback(struct bdi_writeback *wb, int force_wait)
global_page_state(NR_UNSTABLE_NFS) +
(inodes_stat.nr_inodes - inodes_stat.nr_unused);

- wb_writeback(wb, nr_pages, NULL, WB_SYNC_NONE, 1);
+ wrote = wb_writeback(wb, nr_pages, NULL, WB_SYNC_NONE, 1);
}
+
+ return wrote;
}

/*
@@ -427,10 +429,28 @@ void wb_do_writeback(struct bdi_writeback *wb, int force_wait)
*/
int bdi_writeback_task(struct bdi_writeback *wb)
{
+ unsigned long last_active = jiffies;
+ unsigned long wait_jiffies = -1UL;
+ long pages_written;
+
while (!kthread_should_stop()) {
- unsigned long wait_jiffies;
+ pages_written = wb_do_writeback(wb, 0);
+
+ if (pages_written)
+ last_active = jiffies;
+ else if (wait_jiffies != -1UL) {
+ unsigned long max_idle;

- wb_do_writeback(wb, 0);
+ /*
+ * Longest period of inactivity that we tolerate. If we
+ * see dirty data again later, the task will get
+ * recreated automatically.
+ */
+ max_idle = max(5UL * 60 * HZ, wait_jiffies);
+ if (time_after(jiffies, max_idle + last_active) &&
+ wb_is_default_task(wb))
+ break;
+ }

wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
set_current_state(TASK_INTERRUPTIBLE);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 90a1910..7a23f2f 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -110,6 +110,11 @@ int bdi_has_dirty_io(struct backing_dev_info *bdi);
extern spinlock_t bdi_lock;
extern struct list_head bdi_list;

+static inline int wb_is_default_task(struct bdi_writeback *wb)
+{
+ return wb == &wb->bdi->wb;
+}
+
static inline int bdi_wblist_needs_lock(struct backing_dev_info *bdi)
{
return test_bit(BDI_wblist_lock, &bdi->state);
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 588a449..e070b91 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -68,7 +68,7 @@ struct writeback_control {
void writeback_inodes(struct writeback_control *wbc);
int inode_wait(void *);
void sync_inodes_sb(struct super_block *, int wait);
-void wb_do_writeback(struct bdi_writeback *wb, int force_wait);
+long wb_do_writeback(struct bdi_writeback *wb, int force_wait);

/* writeback.h requires fs.h; it, too, is not included from here. */
static inline void wait_on_inode(struct inode *inode)
--
1.6.4.1.207.g68ea


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