[PATCH 8/8 RFC] mm/memcontrol: remove unused memcg_stock code

[Joshua Hahn <joshua.hahnjy@gmail.com>]

Now that all memcg_stock logic has been moved to page_counter_stock, we
can remove all code related to handling memcg_stock. Note that obj_stock
is untouched and is still needed. FLUSHING_CACHED_CHARGE is preserved
so that it can be used by obj_stock as well.

Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
---
 mm/memcontrol.c | 183 ------------------------------------------------
 1 file changed, 183 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4be1638dde180..7de23ecd7cef6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1989,24 +1989,7 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg)
 	pr_cont(" are going to be killed due to memory.oom.group set\n");
 }
 
-/*
- * The value of NR_MEMCG_STOCK is selected to keep the cached memcgs and their
- * nr_pages in a single cacheline. This may change in future.
- */
-#define NR_MEMCG_STOCK 7
 #define FLUSHING_CACHED_CHARGE	0
-struct memcg_stock_pcp {
-	local_trylock_t lock;
-	uint8_t nr_pages[NR_MEMCG_STOCK];
-	struct mem_cgroup *cached[NR_MEMCG_STOCK];
-
-	struct work_struct work;
-	unsigned long flags;
-};
-
-static DEFINE_PER_CPU_ALIGNED(struct memcg_stock_pcp, memcg_stock) = {
-	.lock = INIT_LOCAL_TRYLOCK(lock),
-};
 
 struct obj_stock_pcp {
 	local_trylock_t lock;
@@ -2030,47 +2013,6 @@ static void drain_obj_stock(struct obj_stock_pcp *stock);
 static bool obj_stock_flush_required(struct obj_stock_pcp *stock,
 				     struct mem_cgroup *root_memcg);
 
-/**
- * consume_stock: Try to consume stocked charge on this cpu.
- * @memcg: memcg to consume from.
- * @nr_pages: how many pages to charge.
- *
- * Consume the cached charge if enough nr_pages are present otherwise return
- * failure. Also return failure for charge request larger than
- * MEMCG_CHARGE_BATCH or if the local lock is already taken.
- *
- * returns true if successful, false otherwise.
- */
-static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
-{
-	struct memcg_stock_pcp *stock;
-	uint8_t stock_pages;
-	bool ret = false;
-	int i;
-
-	if (nr_pages > MEMCG_CHARGE_BATCH ||
-	    !local_trylock(&memcg_stock.lock))
-		return ret;
-
-	stock = this_cpu_ptr(&memcg_stock);
-
-	for (i = 0; i < NR_MEMCG_STOCK; ++i) {
-		if (memcg != READ_ONCE(stock->cached[i]))
-			continue;
-
-		stock_pages = READ_ONCE(stock->nr_pages[i]);
-		if (stock_pages >= nr_pages) {
-			WRITE_ONCE(stock->nr_pages[i], stock_pages - nr_pages);
-			ret = true;
-		}
-		break;
-	}
-
-	local_unlock(&memcg_stock.lock);
-
-	return ret;
-}
-
 static void memcg_uncharge(struct mem_cgroup *memcg, unsigned int nr_pages)
 {
 	page_counter_uncharge(&memcg->memory, nr_pages);
@@ -2078,51 +2020,6 @@ static void memcg_uncharge(struct mem_cgroup *memcg, unsigned int nr_pages)
 		page_counter_uncharge(&memcg->memsw, nr_pages);
 }
 
-/*
- * Returns stocks cached in percpu and reset cached information.
- */
-static void drain_stock(struct memcg_stock_pcp *stock, int i)
-{
-	struct mem_cgroup *old = READ_ONCE(stock->cached[i]);
-	uint8_t stock_pages;
-
-	if (!old)
-		return;
-
-	stock_pages = READ_ONCE(stock->nr_pages[i]);
-	if (stock_pages) {
-		memcg_uncharge(old, stock_pages);
-		WRITE_ONCE(stock->nr_pages[i], 0);
-	}
-
-	css_put(&old->css);
-	WRITE_ONCE(stock->cached[i], NULL);
-}
-
-static void drain_stock_fully(struct memcg_stock_pcp *stock)
-{
-	int i;
-
-	for (i = 0; i < NR_MEMCG_STOCK; ++i)
-		drain_stock(stock, i);
-}
-
-static void drain_local_memcg_stock(struct work_struct *dummy)
-{
-	struct memcg_stock_pcp *stock;
-
-	if (WARN_ONCE(!in_task(), "drain in non-task context"))
-		return;
-
-	local_lock(&memcg_stock.lock);
-
-	stock = this_cpu_ptr(&memcg_stock);
-	drain_stock_fully(stock);
-	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
-
-	local_unlock(&memcg_stock.lock);
-}
-
 static void drain_local_obj_stock(struct work_struct *dummy)
 {
 	struct obj_stock_pcp *stock;
@@ -2139,86 +2036,6 @@ static void drain_local_obj_stock(struct work_struct *dummy)
 	local_unlock(&obj_stock.lock);
 }
 
-static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
-{
-	struct memcg_stock_pcp *stock;
-	struct mem_cgroup *cached;
-	uint8_t stock_pages;
-	bool success = false;
-	int empty_slot = -1;
-	int i;
-
-	/*
-	 * For now limit MEMCG_CHARGE_BATCH to 127 and less. In future if we
-	 * decide to increase it more than 127 then we will need more careful
-	 * handling of nr_pages[] in struct memcg_stock_pcp.
-	 */
-	BUILD_BUG_ON(MEMCG_CHARGE_BATCH > S8_MAX);
-
-	VM_WARN_ON_ONCE(mem_cgroup_is_root(memcg));
-
-	if (nr_pages > MEMCG_CHARGE_BATCH ||
-	    !local_trylock(&memcg_stock.lock)) {
-		/*
-		 * In case of larger than batch refill or unlikely failure to
-		 * lock the percpu memcg_stock.lock, uncharge memcg directly.
-		 */
-		memcg_uncharge(memcg, nr_pages);
-		return;
-	}
-
-	stock = this_cpu_ptr(&memcg_stock);
-	for (i = 0; i < NR_MEMCG_STOCK; ++i) {
-		cached = READ_ONCE(stock->cached[i]);
-		if (!cached && empty_slot == -1)
-			empty_slot = i;
-		if (memcg == READ_ONCE(stock->cached[i])) {
-			stock_pages = READ_ONCE(stock->nr_pages[i]) + nr_pages;
-			WRITE_ONCE(stock->nr_pages[i], stock_pages);
-			if (stock_pages > MEMCG_CHARGE_BATCH)
-				drain_stock(stock, i);
-			success = true;
-			break;
-		}
-	}
-
-	if (!success) {
-		i = empty_slot;
-		if (i == -1) {
-			i = get_random_u32_below(NR_MEMCG_STOCK);
-			drain_stock(stock, i);
-		}
-		css_get(&memcg->css);
-		WRITE_ONCE(stock->cached[i], memcg);
-		WRITE_ONCE(stock->nr_pages[i], nr_pages);
-	}
-
-	local_unlock(&memcg_stock.lock);
-}
-
-static bool is_memcg_drain_needed(struct memcg_stock_pcp *stock,
-				  struct mem_cgroup *root_memcg)
-{
-	struct mem_cgroup *memcg;
-	bool flush = false;
-	int i;
-
-	rcu_read_lock();
-	for (i = 0; i < NR_MEMCG_STOCK; ++i) {
-		memcg = READ_ONCE(stock->cached[i]);
-		if (!memcg)
-			continue;
-
-		if (READ_ONCE(stock->nr_pages[i]) &&
-		    mem_cgroup_is_descendant(memcg, root_memcg)) {
-			flush = true;
-			break;
-		}
-	}
-	rcu_read_unlock();
-	return flush;
-}
-
 static void schedule_drain_work(int cpu, struct work_struct *work)
 {
 	/*
-- 
2.52.0