Re: [PATCH v10 3/8] hugetlb_cgroup: add reservation accounting for private mappings

[Mina Almasry <almasrymina@google.com>]

On Wed, Jan 29, 2020 at 1:28 PM David Rientjes <rientjes@google.com> wrote:
>
> On Tue, 14 Jan 2020, Mina Almasry wrote:
>
> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index dea6143aa0685..5491932ea5758 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -46,6 +46,16 @@ struct resv_map {
> >       long adds_in_progress;
> >       struct list_head region_cache;
> >       long region_cache_count;
> > +#ifdef CONFIG_CGROUP_HUGETLB
> > +     /*
> > +      * On private mappings, the counter to uncharge reservations is stored
> > +      * here. If these fields are 0, then either the mapping is shared, or
> > +      * cgroup accounting is disabled for this resv_map.
> > +      */
> > +     struct page_counter *reservation_counter;
> > +     unsigned long pages_per_hpage;
> > +     struct cgroup_subsys_state *css;
> > +#endif
> >  };
> >  extern struct resv_map *resv_map_alloc(void);
> >  void resv_map_release(struct kref *ref);
> > diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
> > index eab8a70d5bcb5..8c320accefe87 100644
> > --- a/include/linux/hugetlb_cgroup.h
> > +++ b/include/linux/hugetlb_cgroup.h
> > @@ -25,6 +25,33 @@ struct hugetlb_cgroup;
> >  #define HUGETLB_CGROUP_MIN_ORDER     2
> >
> >  #ifdef CONFIG_CGROUP_HUGETLB
> > +enum hugetlb_memory_event {
> > +     HUGETLB_MAX,
> > +     HUGETLB_NR_MEMORY_EVENTS,
> > +};
> > +
> > +struct hugetlb_cgroup {
> > +     struct cgroup_subsys_state css;
> > +
> > +     /*
> > +      * the counter to account for hugepages from hugetlb.
> > +      */
> > +     struct page_counter hugepage[HUGE_MAX_HSTATE];
> > +
> > +     /*
> > +      * the counter to account for hugepage reservations from hugetlb.
> > +      */
> > +     struct page_counter reserved_hugepage[HUGE_MAX_HSTATE];
> > +
> > +     atomic_long_t events[HUGE_MAX_HSTATE][HUGETLB_NR_MEMORY_EVENTS];
> > +     atomic_long_t events_local[HUGE_MAX_HSTATE][HUGETLB_NR_MEMORY_EVENTS];
> > +
> > +     /* Handle for "hugetlb.events" */
> > +     struct cgroup_file events_file[HUGE_MAX_HSTATE];
> > +
> > +     /* Handle for "hugetlb.events.local" */
> > +     struct cgroup_file events_local_file[HUGE_MAX_HSTATE];
> > +};
> >
> >  static inline struct hugetlb_cgroup *hugetlb_cgroup_from_page(struct page *page,
> >                                                             bool reserved)
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 62a4cf3db4090..f1b63946ee95c 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -666,6 +666,17 @@ struct resv_map *resv_map_alloc(void)
> >       INIT_LIST_HEAD(&resv_map->regions);
> >
> >       resv_map->adds_in_progress = 0;
> > +#ifdef CONFIG_CGROUP_HUGETLB
> > +     /*
> > +      * Initialize these to 0. On shared mappings, 0's here indicate these
> > +      * fields don't do cgroup accounting. On private mappings, these will be
> > +      * re-initialized to the proper values, to indicate that hugetlb cgroup
> > +      * reservations are to be un-charged from here.
> > +      */
> > +     resv_map->reservation_counter = NULL;
> > +     resv_map->pages_per_hpage = 0;
> > +     resv_map->css = NULL;
> > +#endif
>
> Might be better to extract out a resv_map_init() that does the
> initialization when CONFIG_CGROUP_HUGETLB is enabled?  Could be used here
> as well as hugetlb_reserve_pages().
>
> >
> >       INIT_LIST_HEAD(&resv_map->region_cache);
> >       list_add(&rg->link, &resv_map->region_cache);
> > @@ -3194,7 +3205,11 @@ static void hugetlb_vm_op_close(struct vm_area_struct *vma)
> >
> >       reserve = (end - start) - region_count(resv, start, end);
> >
> > -     kref_put(&resv->refs, resv_map_release);
> > +#ifdef CONFIG_CGROUP_HUGETLB
> > +     hugetlb_cgroup_uncharge_counter(resv->reservation_counter,
> > +                                     (end - start) * resv->pages_per_hpage,
> > +                                     resv->css);
> > +#endif
> >
> >       if (reserve) {
> >               /*
>
> Mike has given is Reviewed-by so likely not a big concern for the generic
> hugetlb code, but I was wondering if we can reduce the number of #ifdef's
> if we defined a CONFIG_CGROUP_HUGETLB helper to take the resv, end, and
> start?  If CONFIG_CGROUP_HUGETLB is defined, it converts into the above,
> otherwise it's a no-op and we don't run into any compile errors because we
> are accessing fields that don't exist without the option.
>

Yes wherever possible I refactored the code a bit to remove #ifdefs in
the middle of hugetlb logic.

> Otherwise looks good!
>
> Acked-by: David Rientjes <rientjes@google.com>