In the node reclaim, may_shrinkslab is 0 by default,
hence shrink_slab will never be performed in it.
While shrik_slab should be performed if the relcaimable slab is over
min slab limit.
If reclaimable pagecache is less than min_unmapped_pages while
reclaimable slab is greater than min_slab_pages, we only shrink slab.
Otherwise the min_unmapped_pages will be useless under this condition.
reclaim_state.reclaimed_slab is to tell us how many pages are
reclaimed in shrink slab.
This issue is very easy to produce, first you continuously cat a random
non-exist file to produce more and more dentry, then you read big file
to produce page cache. And finally you will find that the denty will
never be shrunk.
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
mm/vmscan.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e0c5669..c624f59 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4157,6 +4157,8 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
p->reclaim_state = &reclaim_state;
if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
+ sc.may_shrinkslab = (pgdat->min_slab_pages <
+ node_page_state(pgdat, NR_SLAB_RECLAIMABLE));
/*
* Free memory by calling shrink node with increasing
* priorities until we have enough memory freed.
@@ -4164,6 +4166,28 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
do {
shrink_node(pgdat, &sc);
} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
+ } else {
+ /*
+ * If the reclaimable pagecache is not greater than
+ * min_unmapped_pages, only reclaim the slab.
+ */
+ struct mem_cgroup *memcg;
+ struct mem_cgroup_reclaim_cookie reclaim = {
+ .pgdat = pgdat,
+ .priority = sc.priority,
+ };
+
+ do {
+ memcg = mem_cgroup_iter(NULL, NULL, &reclaim);
+ do {
+ shrink_slab(sc.gfp_mask, pgdat->node_id,
+ memcg, sc.priority);
+ } while ((memcg = mem_cgroup_iter(NULL, memcg,
+ &reclaim)));
+
+ sc.nr_reclaimed += reclaim_state.reclaimed_slab;
+ reclaim_state.reclaimed_slab = 0;
+ } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
}
p->reclaim_state = NULL;
--
1.8.3.1
