From: z00281421 <z00281421@xxxxxxxxxxxxxxxxxxxx>
bdi flusher may enter page alloc slow path due to writepage and kmalloc.
in that case the flusher as a direct reclaimer should not be throttled here
because it can not to reclaim clean file pages or anaonymous pages
for next moment; furthermore writeback rate of dirty pages would be
slow down and other direct reclaimers and kswapd would be affected.
bdi flusher should be iosceduled by get_request rather than here.
Signed-off-by: z00281421 <z00281421@xxxxxxxxxxxxxxxxxxxx>
---
fs/fs-writeback.c | 4 ++--
include/linux/sched.h | 1 +
mm/vmscan.c | 15 +++++++++++----
3 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 05713a5..f6bf067 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1908,7 +1908,7 @@ void wb_workfn(struct work_struct *work)
long pages_written;
set_worker_desc("flush-%s", dev_name(wb->bdi->dev));
- current->flags |= PF_SWAPWRITE;
+ current->flags |= (PF_SWAPWRITE | PF_BDI_FLUSHER | PF_LESS_THROTTLE);
if (likely(!current_is_workqueue_rescuer() ||
!test_bit(WB_registered, &wb->state))) {
@@ -1938,7 +1938,7 @@ void wb_workfn(struct work_struct *work)
else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
wb_wakeup_delayed(wb);
- current->flags &= ~PF_SWAPWRITE;
+ current->flags &= ~(PF_SWAPWRITE | PF_BDI_FLUSHER | PF_LESS_THROTTLE);
}
/*
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 62c68e5..4bb70f2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2232,6 +2232,7 @@ extern void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut,
#define PF_KTHREAD 0x00200000 /* I am a kernel thread */
#define PF_RANDOMIZE 0x00400000 /* randomize virtual address space */
#define PF_SWAPWRITE 0x00800000 /* Allowed to write to swap */
+#define PF_BDI_FLUSHER 0x01000000 /* I am bdi flusher */
#define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_allowed */
#define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */
#define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0fe8b71..492e9e7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1643,12 +1643,19 @@ putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
* If a kernel thread (such as nfsd for loop-back mounts) services
* a backing device by writing to the page cache it sets PF_LESS_THROTTLE.
* In that case we should only throttle if the backing device it is
- * writing to is congested. In other cases it is safe to throttle.
+ * writing to is congested. another case is that bdi flusher could
+ * not be throttled here even though whose bdi is consgested.
+ * In other cases it is safe to throttle.
*/
-static int current_may_throttle(void)
+static bool current_may_throttle(void)
{
- return !(current->flags & PF_LESS_THROTTLE) ||
- current->backing_dev_info == NULL ||
+ if (!(current->flags & PF_LESS_THROTTLE))
+ return true;
+
+ if (current->flags & PF_BDI_FLUSHER)
+ return false;
+
+ return current->backing_dev_info == NULL ||
bdi_write_congested(current->backing_dev_info);
}
--
1.7.9.5
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