linux-kernel - [PATCH 2/2] mem_cgroup: introduce foreign_writeback_in

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Date:   Fri, 24 Sep 2021 14:46:23 +0800
From:   brookxu <brookxu.cn@...il.com>
To:     hannes@...xchg.org, mhocko@...nel.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: [PATCH 2/2] mem_cgroup: introduce foreign_writeback_in_process() function

From: Chunguang Xu <brookxu@...cent.com>

Directly use atomic_read(&frn->done.cnt) == 1 to check whether frn
is issued, which makes the code a bit obscure. Maybe we should
replace it with a more understandable function.

Signed-off-by: Chunguang Xu <brookxu@...cent.com>
---
 mm/memcontrol.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3e1384a6..464745b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4542,6 +4542,12 @@ void mem_cgroup_wb_stats(struct bdi_writeback *wb, unsigned long *pfilepages,
  * As being wrong occasionally doesn't matter, updates and accesses to the
  * records are lockless and racy.
  */
+
+static inline bool foreign_writeback_in_process(struct memcg_cgwb_frn *frn)
+{
+	return atomic_read(&frn->done.cnt) != 1;
+}
+
 void mem_cgroup_track_foreign_dirty_slowpath(struct page *page,
 					     struct bdi_writeback *wb)
 {
@@ -4565,7 +4571,7 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct page *page,
 		    frn->memcg_id == wb->memcg_css->id)
 			break;
 		if (time_before64(frn->at, oldest_at) &&
-		    atomic_read(&frn->done.cnt) == 1) {
+		    !foreign_writeback_in_process(frn)) {
 			oldest = i;
 			oldest_at = frn->at;
 		}
@@ -4612,7 +4618,7 @@ void mem_cgroup_flush_foreign(struct bdi_writeback *wb)
 		 * already one in flight.
 		 */
 		if (time_after64(frn->at, now - intv) &&
-		    atomic_read(&frn->done.cnt) == 1) {
+		    !foreign_writeback_in_process(frn)) {
 			frn->at = 0;
 			trace_flush_foreign(wb, frn->bdi_id, frn->memcg_id);
 			cgroup_writeback_by_id(frn->bdi_id, frn->memcg_id,
-- 
1.8.3.1