[PATCH v6 5/5] mm/memcontrol: add stock to the memsw page counter

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

Attach legacy memsw page counters to their own seven-slot per-CPU
stock. Charge, refill, drain, and hotplug handling now operate on the
memory and memsw banks independently.

Factor the common drain scheduling into schedule_stock_drain() now
that both stocks use it.

Keep the existing direct memsw rollback when the memory charge fails,
ensuring that failed allocations do not replenish the newly
attached memsw stock.

The separate banks can hit, contend, evict, and drain independently,
so their raw counters can temporarily drift by their cached amounts.
The previous patch preserves the user-visible cgroup-v1 invariant by
reporting memory.memsw.usage_in_bytes as the larger raw value.

Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
---
 mm/memcontrol.c | 62 ++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 46 insertions(+), 16 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1a209ad535540..7d5b2539c5699 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2056,6 +2056,13 @@ static DEFINE_PER_CPU_ALIGNED(struct page_counter_stock_pcp, memory_stock) = {
 	.base = &memory_stock,
 };
 
+#ifdef CONFIG_MEMCG_V1
+static DEFINE_PER_CPU_ALIGNED(struct page_counter_stock_pcp, memsw_stock) = {
+	.lock = INIT_LOCAL_TRYLOCK(lock),
+	.base = &memsw_stock,
+};
+#endif
+
 /*
  * NR_OBJ_STOCK is sized so the entire hot path of obj_stock_pcp
  * (lock, accounting metadata, nr_bytes[] and cached[]) fits within a
@@ -2160,12 +2167,30 @@ static bool schedule_drain_work(int cpu, struct work_struct *work)
 	return true;
 }
 
+static void schedule_stock_drain(struct page_counter_stock_pcp __percpu *stock,
+				 struct cgroup_subsys_state *root_css,
+				 int cpu, int curcpu)
+{
+	struct page_counter_stock_pcp *pcp_stock = per_cpu_ptr(stock, cpu);
+
+	if (test_bit(FLUSHING_CACHED_CHARGE, &pcp_stock->flags) ||
+	    !page_counter_stock_flush_required(pcp_stock, root_css) ||
+	    test_and_set_bit(FLUSHING_CACHED_CHARGE, &pcp_stock->flags))
+		return;
+
+	if (cpu == curcpu)
+		drain_local_stock(&pcp_stock->work);
+	else if (!schedule_drain_work(cpu, &pcp_stock->work))
+		clear_bit(FLUSHING_CACHED_CHARGE, &pcp_stock->flags);
+}
+
 /*
  * Drains all per-CPU charge caches for given root_memcg resp. subtree
  * of the hierarchy under it.
  */
 void drain_all_stock(struct mem_cgroup *root_memcg)
 {
+	struct cgroup_subsys_state *root_css = &root_memcg->css;
 	int cpu, curcpu;
 
 	/* If someone's already draining, avoid adding running more workers. */
@@ -2180,21 +2205,13 @@ void drain_all_stock(struct mem_cgroup *root_memcg)
 	migrate_disable();
 	curcpu = smp_processor_id();
 	for_each_online_cpu(cpu) {
-		struct page_counter_stock_pcp *memory_st =
-			per_cpu_ptr(&memory_stock, cpu);
 		struct obj_stock_pcp *obj_st = &per_cpu(obj_stock, cpu);
 
-		if (!test_bit(FLUSHING_CACHED_CHARGE, &memory_st->flags) &&
-		    page_counter_stock_flush_required(memory_st,
-						      &root_memcg->css) &&
-		    !test_and_set_bit(FLUSHING_CACHED_CHARGE,
-				      &memory_st->flags)) {
-			if (cpu == curcpu)
-				drain_local_stock(&memory_st->work);
-			else if (!schedule_drain_work(cpu, &memory_st->work))
-				clear_bit(FLUSHING_CACHED_CHARGE,
-					  &memory_st->flags);
-		}
+		schedule_stock_drain(&memory_stock, root_css, cpu, curcpu);
+#ifdef CONFIG_MEMCG_V1
+		if (do_memsw_account())
+			schedule_stock_drain(&memsw_stock, root_css, cpu, curcpu);
+#endif
 
 		if (!test_bit(FLUSHING_CACHED_CHARGE, &obj_st->flags) &&
 		    obj_stock_flush_required(obj_st, root_memcg) &&
@@ -2221,6 +2238,11 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu)
 	stock = per_cpu_ptr(&memory_stock, cpu);
 	page_counter_drain_stock_fully(stock);
 	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
+#ifdef CONFIG_MEMCG_V1
+	stock = per_cpu_ptr(&memsw_stock, cpu);
+	page_counter_drain_stock_fully(stock);
+	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
+#endif
 
 	/*
 	 * A drain work queued before the CPU went away is executed by an
@@ -2524,8 +2546,8 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 retry:
 	reclaim_options = MEMCG_RECLAIM_MAY_SWAP;
 	if (do_memsw_account() &&
-	    !page_counter_try_charge(&memcg->memsw, nr_pages, &counter, false,
-				     NULL)) {
+	    !page_counter_try_charge(&memcg->memsw, nr_pages, &counter,
+				     may_batch, NULL)) {
 		mem_over_limit = mem_cgroup_from_counter(counter, memsw);
 		reclaim_options &= ~MEMCG_RECLAIM_MAY_SWAP;
 		goto reclaim;
@@ -3004,7 +3026,7 @@ static void obj_cgroup_uncharge_pages(struct obj_cgroup *objcg,
 	if (!mem_cgroup_is_root(memcg)) {
 		page_counter_refill_stock(&memcg->memory, nr_pages);
 		if (do_memsw_account())
-			page_counter_uncharge(&memcg->memsw, nr_pages);
+			page_counter_refill_stock(&memcg->memsw, nr_pages);
 	}
 
 	css_put(&memcg->css);
@@ -4108,6 +4130,10 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 		memcg->memory.stock_css = &memcg->css;
 		page_counter_init(&memcg->swap, &parent->swap, false);
 #ifdef CONFIG_MEMCG_V1
+		if (!memcg_on_dfl) {
+			memcg->memsw.stock = &memsw_stock;
+			memcg->memsw.stock_css = &memcg->css;
+		}
 		WRITE_ONCE(memcg->swappiness, mem_cgroup_swappiness(parent));
 		memcg->memory.track_failcnt = !memcg_on_dfl;
 		memcg->memsw.track_failcnt = !memcg_on_dfl;
@@ -5735,6 +5761,10 @@ int __init mem_cgroup_init(void)
 	for_each_possible_cpu(cpu) {
 		INIT_WORK(&per_cpu_ptr(&memory_stock, cpu)->work,
 			  drain_local_stock);
+#ifdef CONFIG_MEMCG_V1
+		INIT_WORK(&per_cpu_ptr(&memsw_stock, cpu)->work,
+			  drain_local_stock);
+#endif
 		INIT_WORK(&per_cpu_ptr(&obj_stock, cpu)->work,
 			  drain_local_obj_stock);
 	}
-- 
2.53.0-Meta