Re: [PATCH v2 2/2] memcg: don't go through the lruvec for folio and kmem lruvec stat updates

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

On Thu, Oct 22, 2026 at 03:39:30PM -0700, Joanne Koong wrote:
> lruvec_stat_mod_folio() and mod_lruvec_kmem_state() already know the memcg
> and the node, but look up the lruvec with mem_cgroup_lruvec() and update
> the stats through mod_lruvec_state(), which reads lruvec->pgdat and
> mem_cgroup_per_node->memcg to get them back. lruvec->pgdat shares a
> 128-byte cacheline pair with lines that the lru_lock holder writes
> constantly (lru_lock or lru_zone_size[], depending on the alignment of
> struct mem_cgroup_per_node), so on CPUs that do spatial prefetching
> these per-folio stat updates contend with the lru_lock holder.
> 
> Pass the memcg and node they already know to mod_memcg_node_state()
> instead.
> 
> On top of the mem_cgroup_per_node rearrangement, on a 2-socket Skylake
> (80 CPUs) with threads faulting in and freeing shmem in a single memcg,
> this improves throughput by about 3% at 20 threads (5.59M -> 5.77M
> pages/sec) and 2% at 80 threads (8.66M -> 8.82M).
> 
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>