On Thu, Oct 29, 2020 at 04:39:21PM +0100, Michal Koutny wrote:
> Hi.
>
> On Mon, Oct 26, 2020 at 04:13:26PM -0700, Roman Gushchin <guro@xxxxxx> wrote:
> > Please note, that in the non-hierarchical mode all objcgs are always
> > reparented to the root memory cgroup, even if the hierarchy has more
> > than 1 level. This patch doesn't change it.
> >
> > The patch also doesn't affect how the hierarchical mode is working,
> > which is the only sane and truly supported mode now.
> I agree with the patch and you can add
> Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx>
>
> However, it effectively switches any users of root.use_hierarchy=0 (if there
> are any, watching the counters of root memcg) into root.use_hierarchy=1.
> So I'd show them the warning even with a single level of cgroups, i.e.
> add this hunk
It's only partially true. The main difference between the hierarchical and
non-hierarchical mode on the following simple example
/
|
A
/ \
B C
is whether A's memory limits are applied to B, and this is not gonna change.
However you're right, it will change some root cgroup's numbers.
>
> @@ -5356,12 +5356,11 @@
> page_counter_init(&memcg->kmem, &root_mem_cgroup->kmem);
> page_counter_init(&memcg->tcpmem, &root_mem_cgroup->tcpmem);
> /*
> - * Deeper hierachy with use_hierarchy == false doesn't make
> + * Hierachy with use_hierarchy == false doesn't make
> * much sense so let cgroup subsystem know about this
> * unfortunate state in our controller.
> */
> - if (parent != root_mem_cgroup)
> - memory_cgrp_subsys.broken_hierarchy = true;
> + memory_cgrp_subsys.broken_hierarchy = true;
> }
>
> /* The following stuff does not apply to the root */
>
> What do you think?
I think it's in a good direction of deprecating the non-hierarchical mode.
Shakeel did propose it too.
I'd also change the displayed message to something similar to we print
for kmem.limit_in_bytes:
pr_warn_once("kmem.limit_in_bytes is deprecated and will be removed. "
"Please report your usecase to linux-mm@xxxxxxxxx if you "
"depend on this functionality.\n");
Thanks!
