[PATCH] doc,cgroup-v2: memory.max is reported in multiples of page size

[PATCH] doc,cgroup-v2: memory.max is reported in multiples of page size

[Vishal Chourasia]

Update documentation for memory.max to clarify that the reported value
is in multiples of the system page_size. The following example
demonstrates this behavior:

  # cd /sys/fs/cgroup/
  # cat cgroup.subtree_control
  cpu io memory pids
  # mkdir mem
  # cd mem
  # echo 8000000 > memory.max
  # cat memory.max
  7995392

  # getconf PAGESIZE
  65536

  # echo $((8000000/65536*65536))
  7995392

Signed-off-by: Vishal Chourasia <vishalc@linux.ibm.com>
---
 Documentation/admin-guide/cgroup-v2.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 1a16ce68a4d7..577d05c03ffa 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1316,6 +1316,9 @@ PAGE_SIZE multiple when read back.
 	Caller could retry them differently, return into userspace
 	as -ENOMEM or silently ignore in cases like disk readahead.
 
+        Note that the value set for memory.max is reported in units
+        corresponding to the system's page size.
+
   memory.reclaim
 	A write-only nested-keyed file which exists for all cgroups.
 
-- 
2.49.0

Re: [PATCH] doc,cgroup-v2: memory.max is reported in multiples of page size

[Michal Koutný]

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Hello.

On Thu, Apr 10, 2025 at 07:04:40PM +0530, Vishal Chourasia <vishalc@linux.ibm.com> wrote:
> Update documentation for memory.max to clarify that the reported value
> is in multiples of the system page_size. The following example
> demonstrates this behavior:

This applies to any of page_counter-based attribute, not only
memory.max.

> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1316,6 +1316,9 @@ PAGE_SIZE multiple when read back.
>  	Caller could retry them differently, return into userspace
>  	as -ENOMEM or silently ignore in cases like disk readahead.
>  
> +        Note that the value set for memory.max is reported in units
> +        corresponding to the system's page size.
> +

There seems to be mismatch in whitespace to surrounding text.

Also the wording would be more precise if it referred to 'multiples',
not 'units' (units are simply bytes).

Michal

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Re: [PATCH] doc,cgroup-v2: memory.max is reported in multiples of page size

[Vishal Chourasia]

On Thu, Apr 10, 2025 at 03:47:06PM +0200, Michal Koutný wrote:
> Hello.
> 
> On Thu, Apr 10, 2025 at 07:04:40PM +0530, Vishal Chourasia <vishalc@linux.ibm.com> wrote:
> > Update documentation for memory.max to clarify that the reported value
> > is in multiples of the system page_size. The following example
> > demonstrates this behavior:
> 
> This applies to any of page_counter-based attribute, not only
> memory.max.
> 
Yes. This is already documented, and I missed it.

From Documentation/admin-api/cgroup-v2.rst:
...
Memory Interface Files
~~~~~~~~~~~~~~~~~~~~~~

All memory amounts are in bytes.  If a value which is not aligned to
PAGE_SIZE is written, the value may be rounded up to the closest
PAGE_SIZE multiple when read back.
...
> > --- a/Documentation/admin-guide/cgroup-v2.rst
> > +++ b/Documentation/admin-guide/cgroup-v2.rst
> > @@ -1316,6 +1316,9 @@ PAGE_SIZE multiple when read back.
> >  	Caller could retry them differently, return into userspace
> >  	as -ENOMEM or silently ignore in cases like disk readahead.
> >  
> > +        Note that the value set for memory.max is reported in units
> > +        corresponding to the system's page size.
> > +
> 
> There seems to be mismatch in whitespace to surrounding text.
> 
> Also the wording would be more precise if it referred to 'multiples',
> not 'units' (units are simply bytes).
> 
> Michal
>
Got it. But, it seems this patch is redundant. So, I won't be sending
another version.

Thanks,
Vishal