On Tue 09-03-21 12:32:55, Matthew Wilcox wrote:
> On Tue, Mar 09, 2021 at 10:02:00AM +0100, Michal Hocko wrote:
[...]
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 913c2b9e5c72..d44dea2b8d22 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -3135,8 +3135,21 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order)
> > if (memcg && !mem_cgroup_is_root(memcg)) {
> > ret = __memcg_kmem_charge(memcg, gfp, 1 << order);
> > if (!ret) {
> > + int nr_pages = 1 << order;
> > page->memcg_data = (unsigned long)memcg |
> > MEMCG_DATA_KMEM;
> > +
> > + /*
> > + * Compound pages are normally split or freed
> > + * via their head pages so memcg_data in in the
> > + * head page should be sufficient but there
> > + * are exceptions to the rule (see __free_pages).
> > + * Non compound pages would need to copy memcg anyway.
> > + */
> > + for (i = 1; i < nr_pages; i++) {
> > + struct page * p = page + i;
> > + p->memcg_data = page->memcg_data
> > + }
> > return 0;
>
> I would condition this loop on if (!(gfp & __GFP_COMP)), but yes, something
> along these lines. I might phrase the comment a little differently ...
>
> /*
> * Compound pages are treated as a single unit,
> * but non-compound pages can be freed individually
> * so each page needs to have its memcg set to get
> * the accounting right.
> */
OK, I must have misunderstood your __free_pages fix then. I thought this
was about compound pages. Btw. again I forgot about css ref counting so
here is an updated version.
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 913c2b9e5c72..ec2c705f38fa 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3133,10 +3133,22 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order)
memcg = get_mem_cgroup_from_current();
if (memcg && !mem_cgroup_is_root(memcg)) {
- ret = __memcg_kmem_charge(memcg, gfp, 1 << order);
+ int nr_pages = 1 << order;
+ ret = __memcg_kmem_charge(memcg, gfp, nr_pages);
if (!ret) {
page->memcg_data = (unsigned long)memcg |
MEMCG_DATA_KMEM;
+ if (nr_pages > 1) {
+ /*
+ * comment goes here
+ */
+ for (i = 1; i < nr_pages; i++) {
+ struct page * p = page + i;
+ p->memcg_data = page->memcg_data
+ }
+ /* Head page reference from get_mem_cgroup_from_current */
+ css_get_many(&memcg->css, nr_pages - 1);
+ }
return 0;
}
css_put(&memcg->css);
--
Michal Hocko
SUSE Labs
