From: Chunguang Xu <brookxu@xxxxxxxxxxx>
In order to track inflight foreign writeback, we init
wb_completion.cnt to 1. For normal writeback, this cause
wb_wait_for_completion() to perform meaningless atomic
operations. Since foreign writebacks rarely occur in most
scenarios, we can init wb_completion.cnt to 0 and set
frn.done.cnt to 1. In this way we can avoid unnecessary
atomic operations.
Signed-off-by: Chunguang Xu <brookxu@xxxxxxxxxxx>
---
fs/fs-writeback.c | 1 -
include/linux/backing-dev-defs.h | 2 +-
mm/memcontrol.c | 7 ++++---
3 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 81ec192..1ef10f2 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -186,7 +186,6 @@ static void wb_queue_work(struct bdi_writeback *wb,
*/
void wb_wait_for_completion(struct wb_completion *done)
{
- atomic_dec(&done->cnt); /* put down the initial count */
wait_event(*done->waitq, !atomic_read(&done->cnt));
}
diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 3320700..38bd571 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -71,7 +71,7 @@ struct wb_completion {
};
#define __WB_COMPLETION_INIT(_waitq) \
- (struct wb_completion){ .cnt = ATOMIC_INIT(1), .waitq = (_waitq) }
+ (struct wb_completion){ .cnt = ATOMIC_INIT(0), .waitq = (_waitq) }
/*
* If one wants to wait for one or more wb_writeback_works, each work's
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b762215..3e1384a6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5168,9 +5168,10 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
#endif
#ifdef CONFIG_CGROUP_WRITEBACK
INIT_LIST_HEAD(&memcg->cgwb_list);
- for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++)
- memcg->cgwb_frn[i].done =
- __WB_COMPLETION_INIT(&memcg_cgwb_frn_waitq);
+ for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++) {
+ atomic_set(&memcg->cgwb_frn[i].done.cnt, 1);
+ memcg->cgwb_frn[i].done.waitq = &memcg_cgwb_frn_waitq;
+ }
#endif
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
spin_lock_init(&memcg->deferred_split_queue.split_queue_lock);
--
1.8.3.1
