Re: [PATCH 1/4] memcg: initiate deprecation of v1 tcp accounting

[Shakeel Butt <shakeel.butt@linux.dev>]

On Wed, Aug 14, 2024 at 01:59:15PM GMT, T.J. Mercier wrote:
> On Wed, Aug 14, 2024 at 1:28 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
> >
> > Memcg v1 provides opt-in TCP memory accounting feature. However it is
> > mostly unused due to its performance impact on the network traffic. In
> > v2, the TCP memory is accounted in the regular memory usage and is
> > transparent to the users but they can observe the TCP memory usage
> > through memcg stats.
> >
> > Let's initiate the deprecation process of memcg v1's tcp accounting
> > functionality and add warnings to gather if there are any users and if
> > there are, collect how they are using it and plan to provide them better
> > alternative in v2.
> >
> > Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
> > ---
> >  Documentation/admin-guide/cgroup-v1/memory.rst | 8 ++++++++
> >  mm/memcontrol-v1.c                             | 3 +++
> >  2 files changed, 11 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
> > index 9cde26d33843..fb6d3e2a6395 100644
> > --- a/Documentation/admin-guide/cgroup-v1/memory.rst
> > +++ b/Documentation/admin-guide/cgroup-v1/memory.rst
> > @@ -105,10 +105,18 @@ Brief summary of control files.
> >   memory.kmem.max_usage_in_bytes      show max kernel memory usage recorded
> >
> >   memory.kmem.tcp.limit_in_bytes      set/show hard limit for tcp buf memory
> > +                                     This knob is deprecated and shouldn't be
> > +                                     used.
> >   memory.kmem.tcp.usage_in_bytes      show current tcp buf memory allocation
> > +                                     This knob is deprecated and shouldn't be
> > +                                     used.
> >   memory.kmem.tcp.failcnt             show the number of tcp buf memory usage
> > +                                     This knob is deprecated and shouldn't be
> > +                                     used.
> >                                      hits limits
> 
> Looks like you split the description (that has weird grammar) here.
> 

Thanks for catching. Bad paste line. Will fix.

> >   memory.kmem.tcp.max_usage_in_bytes  show max tcp buf memory usage recorded
> > +                                     This knob is deprecated and shouldn't be
> > +                                     used.
> >  ==================================== ==========================================
> >
> >  1. History
> > diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
> > index 9725c731fb21..b8e2ee454eaa 100644
> > --- a/mm/memcontrol-v1.c
> > +++ b/mm/memcontrol-v1.c
> > @@ -2447,6 +2447,9 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
> >                         ret = 0;
> >                         break;
> >                 case _TCP:
> > +                       pr_warn_once("kmem.tcp.limit_in_bytes is deprecated and will be removed. "
> > +                                    "Please report your usecase to linux-mm@kvack.org if you "
> > +                                    "depend on this functionality.\n");
> >                         ret = memcg_update_tcp_max(memcg, nr_pages);
> >                         break;
> >                 }
> > --
> > 2.43.5
> >
> Otherwise LGTM
> Reviewed-by: T.J. Mercier <tjmercier@google.com>

Thanks.