A bit late but let me still propose a session on topics related to memory cgroups. Last year at LSFMM 2024, we discussed [1] about the potential deprecation of memcg v1. Since then we have made very good progress in that regard. We have moved the v1-only code in a separate file and make it not compile by default, have added warnings in many v1-only interfaces and have removed a lot of v1-only code. This year, I want to focus on performance of memory cgroup, particularly improving cost of charging and stats. At the high level we can partition the memory charging in three cases. First is the user memory (anon & file), second if kernel memory (slub mostly) and third is network memory. For network memory, [1] has described some of the challenges. Similarly for kernel memory, we had to revert patches where memcg charging was too expensive [3,4]. I want to discuss and brainstorm different ways to further optimize the memcg charging for all these types of memory. I am at the moment prototying multi-memcg support for per-cpu memcg stocks and would like to see what else we can do. One additional interesting observation from our fleet is that the cost of memory charging increases for the users of memory.low and memory.min. Basically propagate_protected_usage() becomes very prominently visible in the perf traces. Other than charging, the memcg stats infra also is very expensive and a lot of CPUs in our fleet are spent on maintaining these stats. Memcg stats use rstat infrastructure which is designed for fast updates and slow readers. The updaters put the cgroup in a per-cpu update tree while the stats readers flushes update trees of all the cpus. For memcg, the flushes has become very expensive and over the years we have added ratelimiting to limit the cost. I want to discuss what else we can do to further improve the memcg stats. Other than the performance of charging and memcg stats, time permitting, we can discuss other memcg topics like new features or something still lacking. [1] https://lwn.net/Articles/974575/ [2] https://lore.kernel.org/all/20250307055936.3988572-1-shakeel.butt@xxxxxxxxx/ [3] 3754707bcc3e ("Revert "memcg: enable accounting for file lock caches"") [4] 0bcfe68b8767 ("Revert "memcg: enable accounting for pollfd and select bits arrays"")
