[PATCH v14-fix 07/11] mm: multi-gen LRU: dial down MAX_LRU_BATCH

[Yu Zhao <yuzhao@google.com>]

A need_resched warning was reported and already fixed by adding a
need_resched() check to walk_pud_range(). Dial down MAX_LRU_BATCH
anyway in the interest of direct reclaim latency.

WARNING: CPU: 22 PID: 2771 at kernel/sched/core.c:3637 scheduler_tick+0x339/0x410
Call Trace:
 <IRQ>
 update_process_times+0x7b/0x90
 tick_sched_timer+0x82/0xd0
 __run_hrtimer+0x81/0x200
 hrtimer_interrupt+0x192/0x450
 smp_apic_timer_interrupt+0xac/0x1d0
 apic_timer_interrupt+0x88/0x90
 </IRQ>
RIP: 0010:walk_pte_range+0x1c2/0x6a0
 walk_pmd_range+0x1ed/0x490
 walk_pud_range+0xe6/0x2b0
 __walk_page_range+0x111/0x690
 walk_page_range+0x4e/0x150
 walk_mm+0x110/0x200
 try_to_inc_max_seq+0xdb/0xb10
 lru_gen_run_cmd+0x153/0x1c0
 lru_gen_run+0x150/0x210
 stale_page_run+0x62/0x730
 kthread+0x148/0x1b0
 ret_from_fork+0x54/0x60

Reported-by: David Rientjes <rientjes@google.com>
Signed-off-by: Yu Zhao <yuzhao@google.com>
---
 include/linux/mmzone.h | 2 +-
 mm/vmscan.c            | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 2b3f273faf68..4c8510f26b02 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -381,7 +381,7 @@ enum {
 };
 
 #define MIN_LRU_BATCH		BITS_PER_LONG
-#define MAX_LRU_BATCH		(MIN_LRU_BATCH * 128)
+#define MAX_LRU_BATCH		(MIN_LRU_BATCH * 64)
 
 /* whether to keep historical stats from evicted generations */
 #ifdef CONFIG_LRU_GEN_STATS
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 77d2d08950ba..2add99eecd0c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4400,7 +4400,7 @@ static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long max_seq,
 	} while (mm);
 done:
 	if (!success) {
-		if (sc->priority < DEF_PRIORITY - 2)
+		if (sc->priority <= DEF_PRIORITY - 2)
 			wait_event_killable(lruvec->mm_state.wait,
 					    max_seq < READ_ONCE(lrugen->max_seq));
 
-- 
2.37.3.968.ga6b4b080e4-goog