mm: zswap: add per-memcg stat for incompressible pages

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/
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>

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 91beaa6798ce02817546fdde8dfa6659bc9415ab..8ad0b27813175ddf716c59cc52b10c71a0132d70 100644 (file)
--- 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 70b685a85bf4cd0e830c9c0253e4d48f75957fe4..5695776f32c83cb524081ff7e5db1e8e092239ce 100644 (file)
--- 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 823ac6a05bf33bda79cb7c36964dc4e1998583a0..75df24ffdf253833d2c616c338cfd26dcd5c0eaa 100644 (file)
--- 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();
 }