[PATCH 8/8 RFC] mm/memcontrol: remove unused memcg_stock code
From: Joshua Hahn
Date: Fri Apr 10 2026 - 17:14:04 EST
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@xxxxxxxxxxx>
Signed-off-by: Joshua Hahn <joshua.hahnjy@xxxxxxxxx>
---
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