memcg: initiate deprecation of v1 tcp accounting

shakeelb · akpm00 · commit d046ff46ee3b · 2024-09-01T20:26:20.000-07:00
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 [1] 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
@@ -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
@@ -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;
 		}
