From b283ba3ddc9f3dfbebb5c739694f129307bdde71 Mon Sep 17 00:00:00 2001
From: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Date: Mon, 3 Nov 2025 15:51:30 +0800
Subject: [PATCH] mm: memcg: add per-memcg zswap writeback stat

[ Upstream commit 7108cc3f765cafd48a6a35f8add140beaecfa75b ]

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

[nphamcs@gmail.com: rename ZSWP_WB to ZSWPWB]
  Link: https://lkml.kernel.org/r/20231205193307.2432803-1-nphamcs@gmail.com
Link: https://lkml.kernel.org/r/20231130194023.4102148-5-nphamcs@gmail.com
Suggested-by: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Leon Huang Fu <leon.huangfu@shopee.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/linux/vm_event_item.h | 1 +
 mm/memcontrol.c               | 1 +
 mm/vmstat.c                   | 1 +
 mm/zswap.c                    | 4 ++++
 4 files changed, 7 insertions(+)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 8abfa1240040..b61796a35d2b 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -145,6 +145,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 #ifdef CONFIG_ZSWAP
 		ZSWPIN,
 		ZSWPOUT,
+		ZSWPWB,
 #endif
 #ifdef CONFIG_X86
 		DIRECT_MAP_LEVEL2_SPLIT,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c61c90ea72a4..03a984287e5b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -700,6 +700,7 @@ static const unsigned int memcg_vm_event_stat[] = {
 #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
 	ZSWPIN,
 	ZSWPOUT,
+	ZSWPWB,
 #endif
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	THP_FAULT_ALLOC,
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 57891697846b..3630c6e2bb41 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1397,6 +1397,7 @@ const char * const vmstat_text[] = {
 #ifdef CONFIG_ZSWAP
 	"zswpin",
 	"zswpout",
+	"zswpwb",
 #endif
 #ifdef CONFIG_X86
 	"direct_map_level2_splits",
diff --git a/mm/zswap.c b/mm/zswap.c
index 69681b9173fd..a3459440fc31 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -674,6 +674,10 @@ static int zswap_reclaim_entry(struct zswap_pool *pool)
 		goto put_unlock;
 	}
 
+	if (entry->objcg)
+		count_objcg_event(entry->objcg, ZSWPWB);
+
+	count_vm_event(ZSWPWB);
 	/*
 	 * Writeback started successfully, the page now belongs to the
 	 * swapcache. Drop the entry from zswap - unless invalidate already