From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 2 Sep 2022 20:16:11 -0700

On Fri, Sep 2, 2022 at 7:50 PM Kuniyuki Iwashima [off-list ref] wrote:

quoted

Ah, exactly.
Then I will add ____cacheline_aligned_in_smp to tw_refcount, instead of
keeping the original order, to avoid invalidation by sysctl_max_tw_buckets
change, which wouldn't be so frequently done though.

 struct inet_timewait_death_row {
-       refcount_t              tw_refcount;
-
-       struct inet_hashinfo    *hashinfo ____cacheline_aligned_in_smp;
+       struct inet_hashinfo    *hashinfo;
+       refcount_t              tw_refcount ____cacheline_aligned_in_smp;
        int                     sysctl_max_tw_buckets;

This would move sysctl_max_tw_buckets in a separate/dedicated cache line :/

-->

{
   refcount_t              tw_refcount;
   /* Padding to avoid false sharing, tw_refcount can be often written */
    struct inet_hashinfo    *hashinfo ____cacheline_aligned_in_smp;
   int                     sysctl_max_tw_buckets;

  .. other read only fields could fit here.

quoted

 };

Explicit alignment of the structure or first field is not needed,
they will already be cache line aligned.

I got it.  I'll add that change.
Thank you so much!