On Thu, Nov 18, 2021 at 8:13 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
>
> On 11/17/21 12:18, Mina Almasry wrote:
> ...
> > diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
> ...
> > @@ -288,11 +317,21 @@ static void __hugetlb_cgroup_commit_charge(int idx, unsigned long nr_pages,
> > struct hugetlb_cgroup *h_cg,
> > struct page *page, bool rsvd)
> > {
> > + unsigned long *usage;
> > +
>
> I assume the use of a pointer is just to make the following WRITE_ONCE
> look better? I prefer the suggestion by Muchun:
>
> unsigned long usage = h_cg->nodeinfo[page_to_nid(page)]->usage[idx];
>
> usage += nr_pages;
> WRITE_ONCE(h_cg->nodeinfo[page_to_nid(page)]->usage[idx], usage);
>
> I had to think for just a second 'why are we using/passing a pointer?'.
> Not insisting we use Muchun's suggestion, it just caused me to think
> a little more than necessary.
At least I have the same question here. For me I think it's
unnecessary to use a pointer.
>
> In any case, I would move the variable usage inside the
> 'if (!rsvd)' block.
>
> > if (hugetlb_cgroup_disabled() || !h_cg)
> > return;
> >
> > __set_hugetlb_cgroup(page, h_cg, rsvd);
> > - return;
> > + if (!rsvd) {
> > + usage = &h_cg->nodeinfo[page_to_nid(page)]->usage[idx];
> > + /*
> > + * This write is not atomic due to fetching *usage and writing
> > + * to it, but that's fine because we call this with
> > + * hugetlb_lock held anyway.
> > + */
> > + WRITE_ONCE(*usage, *usage + nr_pages);
> > + }
> > }
> >
> > void hugetlb_cgroup_commit_charge(int idx, unsigned long nr_pages,
> > @@ -316,6 +355,7 @@ static void __hugetlb_cgroup_uncharge_page(int idx, unsigned long nr_pages,
> > struct page *page, bool rsvd)
> > {
> > struct hugetlb_cgroup *h_cg;
> > + unsigned long *usage;
>
> Same here.
>
> Otherwise, looks good to me.
> --
> Mike Kravetz
