Re: [PATCH v2 0/6] memcg: Batch mod_memcg_state() for MEMCG_SOCK.

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

On Wed, Oct 28, 2026 at 06:50:12PM +0000, Kuniyuki Iwashima wrote:
> On our production fleet, we saw mem_cgroup_sk_charge() spent over
> 3x the cycles of try_charge_memcg() although the former should be
> a thin wrapper of the latter.
> 
> Looking at perf during tcp_rr, most of the cycles were spent in
> mod_memcg_state(MEMCG_SOCK), which incurred two heavy memory stalls
> due to cache line misses. (see patch 4)
> 
> Also, tcp_rr w/ 20000 flows throughput often degrades by ~50% on
> many core machine. (see patch 5)
> 
> This series adds nr_sock[] to struct memcg_stock_pcp to batch
> mod_memcg_state() for MEMCG_SOCK and move heavy operations to
> out of local_lock(&memcg_stock.lock).
> 
> With this series, tcp_rr w/ 10000 flows achieves 31% more
> throughput with lower latency on machine w/ AMD EPYC 7B12 64-Core
> Processor (Zen 2 Rome, 2 sockets, 256 vCPU)
> 
>   tcp_rr (10000 flows, 128 threads, 60s, average of 3 runs):
> 
>   Metric                     |       Baseline |        Patched |    Diff
>   ---------------------------+----------------+----------------+--------
>   Throughput (RPS)           |     20,884,499 |     27,466,490 | +31.52%
>   Latency Mean (us)          |         478.46 |         363.71 | -23.98%
>   Latency p50 (us)           |         453.96 |         356.68 | -21.43%
>   Latency p90 (us)           |         669.00 |         479.56 | -28.32%
>   Latency p99 (us)           |         969.38 |         617.80 | -36.27%
> 
> 
> Changes:
>   v2:
>     * Rebased on mm.git/mm-new
>     * Add patch 5 for flaky throughput issue
>     * Patch 4:
>       * Benchmark again after rebase and update numbers
>       * Check in_nmi() in __refill_stock()
> 
>   v1: https://lore.kernel.org/linux-mm/20261016052811.3085635-1-kuniyu@google.com/
> 
> 
> Kuniyuki Iwashima (6):
>   memcg: Remove unnecessary READ_ONCE() under memcg_stock.lock.
>   memcg: Reduce nesting in consume_stock() and refill_stock().
>   memcg: Annotate slow paths in consume_stock() and refill_stock().
>   memcg: Batch mod_memcg_state() for MEMCG_SOCK.
>   memcg: Uncharge pages outside memcg_stock.lock in __refill_stock().
>   selftests: cgroup: Deflake test_memcg_sock() in test_memcontrol.c.

Decouple the 4th patch (batch MEMCG_STOCK) from the remaining and send the
remaining patches separately and upfront.

For the 4th patch, I would prefer we first try to move the network sockets
from memcg to objcg path. Then I would prefer we optimize the stats update for
all stats instead of special casing for MEMCG_STOCK.