[PATCH 1/5] mm: memcg: factor out trylock_stock() and unlock_stock()

[Johannes Weiner <hannes@cmpxchg.org>]

From: Johannes Weiner <jweiner@meta.com>

Consolidate the local lock acquisition and the local stock
lookup. This allows subsequent patches to use !!stock as an easy way
to disambiguate the locked vs. contended cases through the callstack.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/memcontrol.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 753d76e96cc6..a975ab3aee10 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3208,6 +3208,19 @@ void __memcg_kmem_uncharge_page(struct page *page, int order)
 	obj_cgroup_put(objcg);
 }
 
+static struct obj_stock_pcp *trylock_stock(void)
+{
+	if (local_trylock(&obj_stock.lock))
+		return this_cpu_ptr(&obj_stock);
+
+	return NULL;
+}
+
+static void unlock_stock(struct obj_stock_pcp *stock)
+{
+	local_unlock(&obj_stock.lock);
+}
+
 static void __account_obj_stock(struct obj_cgroup *objcg,
 				struct obj_stock_pcp *stock, int nr,
 				struct pglist_data *pgdat, enum node_stat_item idx)
@@ -3263,10 +3276,10 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 	struct obj_stock_pcp *stock;
 	bool ret = false;
 
-	if (!local_trylock(&obj_stock.lock))
+	stock = trylock_stock();
+	if (!stock)
 		return ret;
 
-	stock = this_cpu_ptr(&obj_stock);
 	if (objcg == READ_ONCE(stock->cached_objcg) && stock->nr_bytes >= nr_bytes) {
 		stock->nr_bytes -= nr_bytes;
 		ret = true;
@@ -3275,7 +3288,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 			__account_obj_stock(objcg, stock, nr_bytes, pgdat, idx);
 	}
 
-	local_unlock(&obj_stock.lock);
+	unlock_stock(stock);
 
 	return ret;
 }
@@ -3366,7 +3379,8 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 	struct obj_stock_pcp *stock;
 	unsigned int nr_pages = 0;
 
-	if (!local_trylock(&obj_stock.lock)) {
+	stock = trylock_stock();
+	if (!stock) {
 		if (pgdat)
 			mod_objcg_mlstate(objcg, pgdat, idx, nr_acct);
 		nr_pages = nr_bytes >> PAGE_SHIFT;
@@ -3375,7 +3389,6 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 		goto out;
 	}
 
-	stock = this_cpu_ptr(&obj_stock);
 	if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */
 		drain_obj_stock(stock);
 		obj_cgroup_get(objcg);
@@ -3395,7 +3408,7 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 		stock->nr_bytes &= (PAGE_SIZE - 1);
 	}
 
-	local_unlock(&obj_stock.lock);
+	unlock_stock(stock);
 out:
 	if (nr_pages)
 		obj_cgroup_uncharge_pages(objcg, nr_pages);
-- 
2.53.0