Re: [PATCH] bpf: use count for prealloc hashtab too

On Fri, Oct 15, 2021 at 11:04 AM Chengming Zhou
[off-list ref] wrote:

We only use count for kmalloc hashtab not for prealloc hashtab, because
__pcpu_freelist_pop() return NULL when no more elem in pcpu freelist.

But the problem is that __pcpu_freelist_pop() will traverse all CPUs and
spin_lock for all CPUs to find there is no more elem at last.

We encountered bad case on big system with 96 CPUs that alloc_htab_elem()
would last for 1ms. This patch use count for prealloc hashtab too,
avoid traverse and spin_lock for all CPUs in this case.

Signed-off-by: Chengming Zhou <redacted>

It's not clear from the commit log what you're solving.
The atomic inc/dec in critical path of prealloc maps hurts performance.
That's why it's not used.