memcg: initiate deprecation of v1 tcp accounting

Patch series "memcg: initiate deprecation of v1 features", v2.

Start the deprecation process of the memcg v1 features which we discussed
during LSFMMBPF 2024 [1].  For now add the warnings to collect the
information on how the current users are using these features.  Next we
will work on providing better alternatives in v2 (if needed) and fully
deprecate these features.

Link: https://lwn.net/Articles/974575
This patch (of 4):

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.

Link: https://lkml.kernel.org/r/20240814220021.3208384-1-shakeel.butt@linux.dev
Link: https://lkml.kernel.org/r/20240814220021.3208384-2-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: T.J. Mercier <tjmercier@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
index 9cde26d33843552c890c0bf894d45092686f4559..0114d758beabe8c293d76011bedaa830c97fbbfd 100644 (file)
--- 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
                                     hits limits
+                                     This knob is deprecated and shouldn't be
+                                     used.
  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 ff972a35ecc56061804a4a6d458425102e519017..89944f83afb3b3294c34734a27bf9f641d880bfd 100644 (file)
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -2534,6 +2534,9 @@ 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;
                }