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 05:41:04PM -0700, Shakeel Butt wrote:
> 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.
> 

MEMCG_SOCK instead of MEMCG_STOCK