[PATCH v4 1/2] mm/list_lru.c: fix list_lru_count_node() to be race free

Sahitya Tummala
2017-06-29T03:39:37Z

list_lru_count_node() iterates over all memcgs to get
the total number of entries on the node but it can race with
memcg_drain_all_list_lrus(), which migrates the entries from
a dead cgroup to another. This can return incorrect number of
entries from list_lru_count_node().

Fix this by keeping track of entries per node and simply return
it in list_lru_count_node().

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
---
include/linux/list_lru.h | 1 +
mm/list_lru.c | 14 ++++++--------
2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index cb0ba9f..fa7fd03 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -44,6 +44,7 @@ struct list_lru_node {
/* for cgroup aware lrus points to per cgroup lists, otherwise NULL */
struct list_lru_memcg *memcg_lrus;
#endif
+ long nr_items;
} ____cacheline_aligned_in_smp;

struct list_lru {
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 234676e..7a40fa2 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -117,6 +117,7 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item)
l = list_lru_from_kmem(nlru, item);
list_add_tail(item, &l->list);
l->nr_items++;
+ nlru->nr_items++;
spin_unlock(&nlru->lock);
return true;
}
@@ -136,6 +137,7 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item)
l = list_lru_from_kmem(nlru, item);
list_del_init(item);
l->nr_items--;
+ nlru->nr_items--;
spin_unlock(&nlru->lock);
return true;
}
@@ -183,15 +185,10 @@ unsigned long list_lru_count_one(struct list_lru *lru,

unsigned long list_lru_count_node(struct list_lru *lru, int nid)
{
- long count = 0;
- int memcg_idx;
+ struct list_lru_node *nlru;

- count += __list_lru_count_one(lru, nid, -1);
- if (list_lru_memcg_aware(lru)) {
- for_each_memcg_cache_index(memcg_idx)
- count += __list_lru_count_one(lru, nid, memcg_idx);
- }
- return count;
+ nlru = &lru->node[nid];
+ return nlru->nr_items;
}
EXPORT_SYMBOL_GPL(list_lru_count_node);

@@ -226,6 +223,7 @@ unsigned long list_lru_count_node(struct list_lru *lru, int nid)
assert_spin_locked(&nlru->lock);
case LRU_REMOVED:
isolated++;
+ nlru->nr_items--;
/*
* If the lru lock has been dropped, our list
* traversal is now invalid and so we have to