Re: memcg memory accounting in vmalloc is broken

Vlastimil Babka
2021-10-07T14:00:21Z

On 10/7/21 10:50, Vasily Averin wrote:
> On 10/7/21 11:16 AM, Michal Hocko wrote:
>> Cc Mel and Uladzislau
>>
>> On Thu 07-10-21 10:13:23, Michal Hocko wrote:
>>> On Thu 07-10-21 11:04:40, Vasily Averin wrote:
>>>> vmalloc was switched to __alloc_pages_bulk but it does not account the memory to memcg.
>>>>
>>>> Is it known issue perhaps?
>>>
>>> No, I think this was just overlooked. Definitely doesn't look
>>> intentional to me.
>
> I use following patch as a quick fix,
> it helps though it is far from ideal and can be optimized.
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b37435c274cf..e6abe2cac159 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5290,6 +5290,12 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
>
> page = __rmqueue_pcplist(zone, 0, ac.migratetype, alloc_flags,
> pcp, pcp_list);
> +
> + if (memcg_kmem_enabled() && (gfp & __GFP_ACCOUNT) && page &&
> + unlikely(__memcg_kmem_charge_page(page, gfp, 0) != 0)) {
> + __free_pages(page, 0);

It's too early for this here, we didn't go through prep_new_page() yet,
minimally the post_alloc_hook() -> set_page_refcounted() part, required for
put_page_testzero() in __free_pages() to work properly, and probably other
stuff.
Either do the full prep+free or a minimal reversion of __rmqueue_pcplist -
something to just put the page back to pcplist. Probably the former so we
don't introduce subtle errors.

> + page = NULL;
> + }
> if (unlikely(!page)) {
> /* Try and get at least one page */
> if (!nr_populated)
>