[RFC PATCH] mm: bail out from psi memstall when cond_resched

[Zhaoyang Huang <huangzhaoyang@xxxxxxxxx>]

Memory reclaiming will run as several seconds in memory constraint system, which
will be deemed as heavy memstall. Have the memory reclaim be more presiced by
bailing out when cond_resched

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
 mm/vmscan.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a815f73..a083c85 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -316,6 +316,15 @@ static inline bool memcg_congested(struct pglist_data *pgdat,
 }
 #endif
 
+static inline void psi_cond_resched(void)
+{
+	unsigned long *flags;
+
+	if (current->flags & PF_MEMSTALL)
+		psi_memstall_leave(&flags);
+	cond_resched();
+	psi_memstall_enter(&flags);
+}
 /*
  * This misses isolated pages which are not accounted for to save counters.
  * As the data only determines if reclaim or compaction continues, it is
@@ -557,7 +566,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 		total_scan -= shrinkctl->nr_scanned;
 		scanned += shrinkctl->nr_scanned;
 
-		cond_resched();
+		psi_cond_resched();
 	}
 
 	if (next_deferred >= scanned)
@@ -714,7 +723,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 
 	up_read(&shrinker_rwsem);
 out:
-	cond_resched();
+	psi_cond_resched();
 	return freed;
 }
 
@@ -1109,7 +1118,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 	unsigned nr_reclaimed = 0;
 
 	memset(stat, 0, sizeof(*stat));
-	cond_resched();
+	psi_cond_resched();
 
 	while (!list_empty(page_list)) {
 		struct address_space *mapping;
@@ -1118,7 +1127,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		enum page_references references = PAGEREF_RECLAIM_CLEAN;
 		bool dirty, writeback;
 
-		cond_resched();
+		psi_cond_resched();
 
 		page = lru_to_page(page_list);
 		list_del(&page->lru);
@@ -2084,7 +2093,7 @@ static void shrink_active_list(unsigned long nr_to_scan,
 	spin_unlock_irq(&pgdat->lru_lock);
 
 	while (!list_empty(&l_hold)) {
-		cond_resched();
+		psi_cond_resched();
 		page = lru_to_page(&l_hold);
 		list_del(&page->lru);
 
@@ -2500,7 +2509,7 @@ static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memc
 			}
 		}
 
-		cond_resched();
+		psi_cond_resched();
 
 		if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
 			continue;
@@ -4149,7 +4158,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
 		.reclaim_idx = gfp_zone(gfp_mask),
 	};
 
-	cond_resched();
+	psi_cond_resched();
 	fs_reclaim_acquire(sc.gfp_mask);
 	/*
 	 * We need to be able to allocate from the reserves for RECLAIM_UNMAP
-- 
1.9.1