Re: [PATCH 5/8] mm: memcontrol: account socket memory on unified hierarchy

Vladimir Davydov
2015-10-22T18:48:17Z

On Thu, Oct 22, 2015 at 12:21:33AM -0400, Johannes Weiner wrote:
...
> @@ -5500,13 +5524,38 @@ void sock_release_memcg(struct sock *sk)
> */
> bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
> {
> + unsigned int batch = max(CHARGE_BATCH, nr_pages);
> struct page_counter *counter;
> + bool force = false;
>
> - if (page_counter_try_charge(&memcg->skmem, nr_pages, &counter))
> + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
> + if (page_counter_try_charge(&memcg->skmem, nr_pages, &counter))
> + return true;
> + page_counter_charge(&memcg->skmem, nr_pages);
> + return false;
> + }
> +
> + if (consume_stock(memcg, nr_pages))
> return true;
> +retry:
> + if (page_counter_try_charge(&memcg->memory, batch, &counter))
> + goto done;

Currently, we use memcg->memory only for charging memory pages. Besides,
every page charged to this counter (including kmem) has ->mem_cgroup
field set appropriately. This looks consistent and nice. As an extra
benefit, we can track all pages charged to a memory cgroup via
/proc/kapgecgroup.

Now, you charge "window size" to it, which AFAIU isn't necessarily equal
to the amount of memory actually consumed by the cgroup for socket
buffers. I think this looks ugly and inconsistent with the existing
behavior. I agree that we need to charge socker buffers to ->memory, but
IMO we should do that per each skb page, using memcg_kmem_charge_kmem
somewhere in alloc_skb_with_frags invoking the reclaimer just as we do
for kmalloc, while tcp window size control should stay aside.

Thanks,
Vladimir