On Wed, 19 Apr 2023 09:20:07 +0000 Haifeng Xu <haifeng.xu@xxxxxxxxxx> wrote:
> There are three places, vmpressure_prio(), shrink_node_memcgs() and
> shrink_node(), which invoke vmpressure(). But only shrink_node_memcgs()
> sets tree to false and the memcg used in it is not NULL, so we don't
> check it again in vmpressure().
>
> ...
>
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -284,7 +284,7 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
> enum vmpressure_levels level;
>
> /* For now, no users for root-level efficiency */
> - if (!memcg || mem_cgroup_is_root(memcg))
> + if (mem_cgroup_is_root(memcg))
> return;
>
> spin_lock(&vmpr->sr_lock);
try_to_free_pages()->
do_try_to_free_pages()->
vmpressure_prio()->
vmpressure()->
crash
what am I missing here?
It does appear that vmpressure() could be simplified with
if (!memcg)
memcg = root_mem_cgroup;
so the test you identified goes away and the memcg_to_vmpressure() call
becomes simpler. But that's such a small change it doesn't seem worth
the effort.
