[PATCH v3 3/5] mm: memcg: add per-memcg zswap writeback stat

[Nhat Pham <nphamcs@gmail.com>]

From: Domenico Cerasuolo <cerasuolodomenico@gmail.com>

Since zswap now writes back pages from memcg-specific LRUs, we now need a
new stat to show writebacks count for each memcg.

Suggested-by: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
---
 include/linux/memcontrol.h |  2 ++
 mm/memcontrol.c            | 15 +++++++++++++++
 mm/zswap.c                 |  3 +++
 3 files changed, 20 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 3de10fabea0f..7868b1e00bf5 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -38,6 +38,7 @@ enum memcg_stat_item {
 	MEMCG_KMEM,
 	MEMCG_ZSWAP_B,
 	MEMCG_ZSWAPPED,
+	MEMCG_ZSWAP_WB,
 	MEMCG_NR_STAT,
 };
 
@@ -1884,6 +1885,7 @@ static inline void count_objcg_event(struct obj_cgroup *objcg,
 bool obj_cgroup_may_zswap(struct obj_cgroup *objcg);
 void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size);
 void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size);
+void obj_cgroup_report_zswap_wb(struct obj_cgroup *objcg);
 #else
 static inline bool obj_cgroup_may_zswap(struct obj_cgroup *objcg)
 {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1bde67b29287..a9118871e5a6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1505,6 +1505,7 @@ static const struct memory_stat memory_stats[] = {
 #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
 	{ "zswap",			MEMCG_ZSWAP_B			},
 	{ "zswapped",			MEMCG_ZSWAPPED			},
+	{ "zswap_wb",			MEMCG_ZSWAP_WB			},
 #endif
 	{ "file_mapped",		NR_FILE_MAPPED			},
 	{ "file_dirty",			NR_FILE_DIRTY			},
@@ -1541,6 +1542,7 @@ static int memcg_page_state_unit(int item)
 	switch (item) {
 	case MEMCG_PERCPU_B:
 	case MEMCG_ZSWAP_B:
+	case MEMCG_ZSWAP_WB:
 	case NR_SLAB_RECLAIMABLE_B:
 	case NR_SLAB_UNRECLAIMABLE_B:
 	case WORKINGSET_REFAULT_ANON:
@@ -7861,6 +7863,19 @@ void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size)
 	rcu_read_unlock();
 }
 
+void obj_cgroup_report_zswap_wb(struct obj_cgroup *objcg)
+{
+	struct mem_cgroup *memcg;
+
+	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return;
+
+	rcu_read_lock();
+	memcg = obj_cgroup_memcg(objcg);
+	mod_memcg_state(memcg, MEMCG_ZSWAP_WB, 1);
+	rcu_read_unlock();
+}
+
 static u64 zswap_current_read(struct cgroup_subsys_state *css,
 			      struct cftype *cft)
 {
diff --git a/mm/zswap.c b/mm/zswap.c
index d2989ad11814..15485427e3fa 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -704,6 +704,9 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o
 	}
 	zswap_written_back_pages++;
 
+	if (entry->objcg)
+		obj_cgroup_report_zswap_wb(entry->objcg);
+
 	/*
 	 * Writeback started successfully, the page now belongs to the
 	 * swapcache. Drop the entry from zswap - unless invalidate already
-- 
2.34.1