Re: [PATCH v3 2/3] mm: Charge active memcg when no mm is set

From: Shakeel Butt
Date: Thu Feb 20 2020 - 16:15:19 EST

On Thu, Feb 20, 2020 at 8:52 AM Dan Schatzberg <schatzberg.dan@xxxxxxxxx> wrote:
> memalloc_use_memcg() worked for kernel allocations but was silently
> ignored for user pages.
> This patch establishes a precedence order for who gets charged:
> 1. If there is a memcg associated with the page already, that memcg is
> charged. This happens during swapin.
> 2. If an explicit mm is passed, mm->memcg is charged. This happens
> during page faults, which can be triggered in remote VMs (eg gup).
> 3. Otherwise consult the current process context. If it has configured
> a current->active_memcg, use that. Otherwise, current->mm->memcg.
> Previously, if a NULL mm was passed to mem_cgroup_try_charge (case 3) it
> would always charge the root cgroup. Now it looks up the current
> active_memcg first (falling back to charging the root cgroup if not
> set).
> Signed-off-by: Dan Schatzberg <schatzberg.dan@xxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Acked-by: Tejun Heo <tj@xxxxxxxxxx>

Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>