On Thu, Oct 31, 2019 at 01:52:44AM +0000, Roman Gushchin wrote:
> On Fri, Oct 25, 2019 at 03:41:18PM -0400, Johannes Weiner wrote:
> > @@ -3117,15 +3095,24 @@ void __memcg_kmem_uncharge(struct page *page, int order)
> > css_put_many(&memcg->css, nr_pages);
> > }
> >
> > -int __memcg_kmem_charge_subpage(struct mem_cgroup *memcg, size_t size,
> > - gfp_t gfp)
> > +int obj_cgroup_charge(struct obj_cgroup *objcg, size_t size, gfp_t gfp)
> > {
> > - return try_charge(memcg, gfp, size, true);
> > + int ret;
> > +
> > + if (consume_obj_stock(objcg, nr_bytes))
> > + return 0;
> > +
> > + ret = try_charge(objcg->memcg, gfp, 1);
> > + if (ret)
> > + return ret;
> The second problem is also here. If a task belonging to a different memcg
> is scheduled on this cpu, most likely we will need to refill both stocks,
> even if we need only a small temporarily allocation.
Yes, that's a good thing. The reason we have the per-cpu caches in the
first place is because most likely the same cgroup will perform
several allocations. Both the slab allocator and the page allocator
have per-cpu caches for the same reason. I don't really understand
what the argument is.
> > +
> > + refill_obj_stock(objcg, PAGE_SIZE - size);
>
> And the third problem is here. Percpu allocations (on which accounting I'm
> working right now) can be larger than a page.
How about this?
nr_pages = round_up(size, PAGE_SIZE);
try_charge(objcg->memcg, nr_pages);
refill_obj_stock(objcg, size % PAGE_SIZE);
> This is fairly small issue in comparison to the first one. But it illustrates
> well the main point: we can't simple get a page from the existing API and
> sublease it in parts. The problem is that we need to break the main principle
> that a page belongs to a single memcg.
We can change the underlying assumptions of the existing API if they
are no longer correct. We don't have to invent a parallel stack.
