[PATCH] mm: fs: invalidate bh_lrus for only cold path

[Minchan Kim]

kernel test robot reported the regression of fio.write_iops[1]
with [2].

Since lru_add_drain is called frequently, invalidate bh_lrus
there could increase bh_lrus cache miss ratio, which needs
more IO in the end.

This patch moves the bh_lrus invalidation from the hot path(
e.g., zap_page_range, pagevec_release) to cold path(i.e.,
lru_add_drain_all, lru_cache_disable).

[1] https://lore.kernel.org/lkml/20210520083144.GD14190@xsang-OptiPlex-9020/
[2] 8cc621d2f45d, mm: fs: invalidate BH LRU during page migration
Cc: Xing, Zhengjun <zhengjun.xing@xxxxxxxxx>
Cc: Chris Goldsworthy <cgoldswo@xxxxxxxxxxxxxx>
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
 mm/swap.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index 1958d5feb148..3e25d99a9dbb 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -642,7 +642,6 @@ void lru_add_drain_cpu(int cpu)
 		pagevec_lru_move_fn(pvec, lru_lazyfree_fn);
 
 	activate_page_drain(cpu);
-	invalidate_bh_lrus_cpu(cpu);
 }
 
 /**
@@ -725,6 +724,17 @@ void lru_add_drain(void)
 	local_unlock(&lru_pvecs.lock);
 }
 
+static void lru_add_and_bh_lrus_drain(void)
+{
+	int cpu;
+
+	local_lock(&lru_pvecs.lock);
+	cpu = smp_processor_id();
+	lru_add_drain_cpu(cpu);
+	local_unlock(&lru_pvecs.lock);
+	invalidate_bh_lrus_cpu(cpu);
+}
+
 void lru_add_drain_cpu_zone(struct zone *zone)
 {
 	local_lock(&lru_pvecs.lock);
@@ -739,7 +749,7 @@ static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
 
 static void lru_add_drain_per_cpu(struct work_struct *dummy)
 {
-	lru_add_drain();
+	lru_add_and_bh_lrus_drain();
 }
 
 /*
@@ -880,7 +890,7 @@ void lru_cache_disable(void)
 	 */
 	__lru_add_drain_all(true);
 #else
-	lru_add_drain();
+	lru_add_and_bh_lrus_drain();
 #endif
 }
 
-- 
2.31.1.818.g46aad6cb9e-goog