[PATCH] Docs/admin-guide/cgroup-v2: fix memory.stat doc details

[PATCH] Docs/admin-guide/cgroup-v2: fix memory.stat doc details

[Doehyun Baek]

Fix minor cgroup v2 memory.stat documentation issues.  Correct the
vmalloc per-node marker now that vmalloc uses the native NR_VMALLOC node
stat, and document zswap_incomp as a byte-valued memory amount instead
of as a page counter.

Fixes: c466412c73c3 ("mm: memcontrol: switch to native NR_VMALLOC vmstat counter")
Fixes: 5ad41a38c364 ("mm: zswap: add per-memcg stat for incompressible pages")
Signed-off-by: Doehyun Baek <doehyunbaek@gmail.com>
---
 Documentation/admin-guide/cgroup-v2.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 993446ab66d0..ce6741f78f4f 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1570,7 +1570,7 @@ The following nested keys are defined.
 	  sock (npn)
 		Amount of memory used in network transmission buffers
 
-	  vmalloc (npn)
+	  vmalloc
 		Amount of memory used for vmap backed memory.
 
 	  shmem
@@ -1735,7 +1735,7 @@ The following nested keys are defined.
 		Number of pages written from zswap to swap.
 
 	  zswap_incomp
-		Number of incompressible pages currently stored in zswap
+		Amount of memory used by 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.
 

base-commit: 1a3746ccbb0a97bed3c06ccde6b880013b1dddc1
-- 
2.43.0

Re: [PATCH] Docs/admin-guide/cgroup-v2: fix memory.stat doc details

[Michal Koutný]

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On Sat, Jun 20, 2026 at 12:27:51PM +0000, Doehyun Baek <doehyunbaek@gmail.com> wrote:
> Fix minor cgroup v2 memory.stat documentation issues.  Correct the
> vmalloc per-node marker now that vmalloc uses the native NR_VMALLOC node
> stat, and document zswap_incomp as a byte-valued memory amount instead
> of as a page counter.
> 
> Fixes: c466412c73c3 ("mm: memcontrol: switch to native NR_VMALLOC vmstat counter")
> Fixes: 5ad41a38c364 ("mm: zswap: add per-memcg stat for incompressible pages")
> Signed-off-by: Doehyun Baek <doehyunbaek@gmail.com>
> ---
>  Documentation/admin-guide/cgroup-v2.rst | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 993446ab66d0..ce6741f78f4f 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1570,7 +1570,7 @@ The following nested keys are defined.
>  	  sock (npn)
>  		Amount of memory used in network transmission buffers
>  
> -	  vmalloc (npn)
> +	  vmalloc
>  		Amount of memory used for vmap backed memory.

The vmalloc change looks OK...

>  
>  	  shmem
> @@ -1735,7 +1735,7 @@ The following nested keys are defined.
>  		Number of pages written from zswap to swap.
>  
>  	  zswap_incomp
> -		Number of incompressible pages currently stored in zswap
> +		Amount of memory used by 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.

...but what do you mean by this?
As I'm looking at the code in obj_cgroup_charge_zswap() and
memcg_page_state_output_unit(), I'd say those are pages and the docs is
thus alright.

Thanks,
Michal

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Re: [PATCH] Docs/admin-guide/cgroup-v2: fix memory.stat doc details

[Doehyun Baek]

> ...but what do you mean by this?
> As I'm looking at the code in obj_cgroup_charge_zswap() and
> memcg_page_state_output_unit(), I'd say those are pages and the docs is
> thus alright.
>
> Thanks,
> Michal

Thanks for taking a look.

I agree that the counters are pages internally. I was talking about what
gets printed in memory.stat.

The internal updates are page-count based:

    mod_memcg_state(memcg, MEMCG_ZSWAPPED, 1);
    if (size == PAGE_SIZE)
        mod_memcg_state(memcg, MEMCG_ZSWAP_INCOMP, 1);

However, both zswapped and zswap_incomp are memory_stats[] entries, so
memory.stat prints them through memcg_page_state_output(). Since
MEMCG_ZSWAP_INCOMP is not special-cased as a raw count, the stored page
count is multiplied by the default PAGE_SIZE unit and exported as bytes.

    unsigned long memcg_page_state_output(struct mem_cgroup *memcg, int item)
    {
        return memcg_page_state(memcg, item) *
        memcg_page_state_output_unit(item);
    }

Separately, this matches the existing documentation style for zswapped,
whose exported value is described as a memory amount:

    zswapped
        Amount of application memory swapped out to zswap.

Since zswap_incomp follows the same memory.stat output path, I think its
documentation should describe the exported value as a memory amount too.

I also boot-tested this in QEMU with the current tree and zswap enabled.
With incompressible pages pushed into zswap, memory.stat showed:

    zswap 87822336
    zswapped 87822336
    zswap_incomp 87822336

The zswap_incomp value there is byte-valued; it is not a plain page
count. It also matches zswapped in this all-incompressible case, which
is consistent with both being exported as memory amounts.

Best,
Doehyun Baek

Re: [PATCH] Docs/admin-guide/cgroup-v2: fix memory.stat doc details

[Michal Koutný]

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On Mon, Jun 22, 2026 at 05:26:53PM +0200, Doehyun Baek <doehyunbaek@gmail.com> wrote:
> However, both zswapped and zswap_incomp are memory_stats[] entries, so
> memory.stat prints them through memcg_page_state_output(). Since
> MEMCG_ZSWAP_INCOMP is not special-cased as a raw count, the stored page
> count is multiplied by the default PAGE_SIZE unit and exported as bytes.
> 
>     unsigned long memcg_page_state_output(struct mem_cgroup *memcg, int item)
>     {
>         return memcg_page_state(memcg, item) *
>         memcg_page_state_output_unit(item);
>     }

Ah, I messed up how memcg_page_state_output_unit() is used. The printed
values are amounts (in bytes).

> Separately, this matches the existing documentation style for zswapped,
> whose exported value is described as a memory amount:
> 
>     zswapped
>         Amount of application memory swapped out to zswap.
> 
> Since zswap_incomp follows the same memory.stat output path, I think its
> documentation should describe the exported value as a memory amount too.
> 
> I also boot-tested this in QEMU with the current tree and zswap enabled.
> With incompressible pages pushed into zswap, memory.stat showed:
> 
>     zswap 87822336
>     zswapped 87822336
>     zswap_incomp 87822336

Thanks for the test and for the fix!

> 
> The zswap_incomp value there is byte-valued; it is not a plain page
> count. It also matches zswapped in this all-incompressible case, which
> is consistent with both being exported as memory amounts.

Acked-by: Michal Koutný <mkoutny@suse.com>

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Re: [PATCH] Docs/admin-guide/cgroup-v2: fix memory.stat doc details

[Nhat Pham]

On Sat, Jun 20, 2026 at 5:28 AM Doehyun Baek <doehyunbaek@gmail.com> wrote:
>
> Fix minor cgroup v2 memory.stat documentation issues.  Correct the
> vmalloc per-node marker now that vmalloc uses the native NR_VMALLOC node
> stat, and document zswap_incomp as a byte-valued memory amount instead
> of as a page counter.
>
> Fixes: c466412c73c3 ("mm: memcontrol: switch to native NR_VMALLOC vmstat counter")
> Fixes: 5ad41a38c364 ("mm: zswap: add per-memcg stat for incompressible pages")
> Signed-off-by: Doehyun Baek <doehyunbaek@gmail.com>
> -               Number of incompressible pages currently stored in zswap
> +               Amount of memory used by 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.
>

Good catch :)

Reviewed-by: Nhat Pham <nphamcs@gmail.com>