From 5ad41a38c36474ff59545cb514801d90719555de Mon Sep 17 00:00:00 2001
From: Jiayuan Chen <jiayuan.chen@shopee.com>
Date: Fri, 13 Feb 2026 15:18:22 +0800
Subject: [PATCH] mm: zswap: add per-memcg stat for incompressible pages
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Patch series "mm: zswap: add per-memcg stat for incompressible pages", v3.

In containerized environments, knowing which cgroup is contributing
incompressible pages to zswap is essential for effective resource
management.  This series adds a new per-memcg stat 'zswap_incomp' to track
incompressible pages, along with a selftest.


This patch (of 2):

The global zswap_stored_incompressible_pages counter was added in commit
dca4437a5861 ("mm/zswap: store <PAGE_SIZE compression failed page as-is")
to track how many pages are stored in raw (uncompressed) form in zswap.
However, in containerized environments, knowing which cgroup is
contributing incompressible pages is essential for effective resource
management [1].

Add a new memcg stat 'zswap_incomp' to track incompressible pages per
cgroup.  This helps administrators and orchestrators to:

1. Identify workloads that produce incompressible data (e.g., encrypted
   data, already-compressed media, random data) and may not benefit from
   zswap.

2. Make informed decisions about workload placement - moving
   incompressible workloads to nodes with larger swap backing devices
   rather than relying on zswap.

3. Debug zswap efficiency issues at the cgroup level without needing to
   correlate global stats with individual cgroups.

While the compression ratio can be estimated from existing stats (zswap /
zswapped * PAGE_SIZE), this doesn't distinguish between "uniformly poor
compression" and "a few completely incompressible pages mixed with highly
compressible ones".  The zswap_incomp stat provides direct visibility into
the latter case.

Link: https://lkml.kernel.org/r/20260213071827.5688-1-jiayuan.chen@linux.dev
Link: https://lkml.kernel.org/r/20260213071827.5688-2-jiayuan.chen@linux.dev
Link: https://lore.kernel.org/linux-mm/CAF8kJuONDFj4NAksaR4j_WyDbNwNGYLmTe-o76rqU17La=nkOw@mail.gmail.com/ [1]
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 Documentation/admin-guide/cgroup-v2.rst | 5 +++++
 include/linux/memcontrol.h              | 1 +
 mm/memcontrol.c                         | 6 ++++++
 3 files changed, 12 insertions(+)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 91beaa6798ce..8ad0b2781317 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1734,6 +1734,11 @@ The following nested keys are defined.
 	  zswpwb
 		Number of pages written from zswap to swap.
 
+	  zswap_incomp
+		Number of incompressible pages currently stored in zswap
+		without compression. These pages could not be compressed to
+		a size smaller than PAGE_SIZE, so they are stored as-is.
+
 	  thp_fault_alloc (npn)
 		Number of transparent hugepages which were allocated to satisfy
 		a page fault. This counter is not present when CONFIG_TRANSPARENT_HUGEPAGE
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 70b685a85bf4..5695776f32c8 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -39,6 +39,7 @@ enum memcg_stat_item {
 	MEMCG_KMEM,
 	MEMCG_ZSWAP_B,
 	MEMCG_ZSWAPPED,
+	MEMCG_ZSWAP_INCOMP,
 	MEMCG_NR_STAT,
 };
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 823ac6a05bf3..75df24ffdf25 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -356,6 +356,7 @@ static const unsigned int memcg_stat_items[] = {
 	MEMCG_KMEM,
 	MEMCG_ZSWAP_B,
 	MEMCG_ZSWAPPED,
+	MEMCG_ZSWAP_INCOMP,
 };
 
 #define NR_MEMCG_NODE_STAT_ITEMS ARRAY_SIZE(memcg_node_stat_items)
@@ -1368,6 +1369,7 @@ static const struct memory_stat memory_stats[] = {
 #ifdef CONFIG_ZSWAP
 	{ "zswap",			MEMCG_ZSWAP_B			},
 	{ "zswapped",			MEMCG_ZSWAPPED			},
+	{ "zswap_incomp",		MEMCG_ZSWAP_INCOMP		},
 #endif
 	{ "file_mapped",		NR_FILE_MAPPED			},
 	{ "file_dirty",			NR_FILE_DIRTY			},
@@ -5520,6 +5522,8 @@ void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size)
 	memcg = obj_cgroup_memcg(objcg);
 	mod_memcg_state(memcg, MEMCG_ZSWAP_B, size);
 	mod_memcg_state(memcg, MEMCG_ZSWAPPED, 1);
+	if (size == PAGE_SIZE)
+		mod_memcg_state(memcg, MEMCG_ZSWAP_INCOMP, 1);
 	rcu_read_unlock();
 }
 
@@ -5543,6 +5547,8 @@ void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size)
 	memcg = obj_cgroup_memcg(objcg);
 	mod_memcg_state(memcg, MEMCG_ZSWAP_B, -size);
 	mod_memcg_state(memcg, MEMCG_ZSWAPPED, -1);
+	if (size == PAGE_SIZE)
+		mod_memcg_state(memcg, MEMCG_ZSWAP_INCOMP, -1);
 	rcu_read_unlock();
 }