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SubjectRe: [PATCH v9 3/8] hugetlb_cgroup: add reservation accounting for private mappings
On Mon, Jan 13, 2020 at 4:55 PM Mike Kravetz <mike.kravetz@oracle.com> wrote:
> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index dea6143aa0685..e6ab499ba2086 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -46,6 +46,15 @@ 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 the mapping is shared.
>
> Will *reservation_counter ALWAYS be non-NULL for private mappings?
>
> More on this below.
>
> > + */
> > + 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 e6e8240f1718c..7782977970301 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -665,6 +665,17 @@ 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
> >
> > INIT_LIST_HEAD(&resv_map->region_cache);
> > list_add(&rg->link, &resv_map->region_cache);
> > @@ -3145,7 +3156,20 @@ 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
> > + /*
> > + * Since we check for HPAGE_RESV_OWNER above, this must a private
> > + * mapping, and these values should be none-zero, and should point to
> > + * the hugetlb_cgroup counter to uncharge for this reservation.
> > + */
> > + WARN_ON(!resv->reservation_counter);
> > + WARN_ON(!resv->pages_per_hpage);
> > + WARN_ON(!resv->css);
>
> I was once again wondering if these were always non-NULL for private mappings.
> It seems that reservation_counter (h_gc) would be NULL in these cases from
> these early checks in hugetlb_cgroup_charge_cgroup().
>

You are right. I'm fixing in v10 the code and comments to account for
h_cg potentially being NULL, but I'm having trouble testing. Looking
at the code, I'm a bit confused by the checks. Seems to me
hugetlb_cgroup_disabled() is the same as #ifdef CONFIG_CGROUP_HUGETLB;
I can't find a way to enable the Kconfig but have that return false
unless I hack the code. Also seems to me checking huge_page_order is
just super definsive; I skimmed the hugepage sizes allowed code and I
can't find an arch that allows you to configure hugetlb page size to <
2^HUGETLB_CGROUP_MIN_ORDER pages. So in reality these will never fire,
IIUC.

> int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
> struct hugetlb_cgroup **ptr, bool reserved)
> {
> int ret = 0;
> struct page_counter *counter;
> struct hugetlb_cgroup *h_cg = NULL;
>
> if (hugetlb_cgroup_disabled())
> goto done;
> /*
> * We don't charge any cgroup if the compound page have less
> * than 3 pages.
> */
> if (huge_page_order(&hstates[idx]) < HUGETLB_CGROUP_MIN_ORDER)
> goto done;
> ...
>
> It seems like the following hugetlb_cgroup_uncharge_counter() guards
> against reservation_counter being NULL (for some of the same reasons).
>
> > +
> > + hugetlb_cgroup_uncharge_counter(resv->reservation_counter,
> > + (end - start) * resv->pages_per_hpage,
> > + resv->css);
> > +#endif
> >
> > if (reserve) {
> > /*
> > @@ -3155,6 +3179,8 @@ static void hugetlb_vm_op_close(struct vm_area_struct *vma)
> > gbl_reserve = hugepage_subpool_put_pages(spool, reserve);
> > hugetlb_acct_memory(h, -gbl_reserve);
> > }
> > +
> > + kref_put(&resv->refs, resv_map_release);
> > }
> >
> > static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
> > @@ -4501,6 +4527,7 @@ int hugetlb_reserve_pages(struct inode *inode,
> > struct hstate *h = hstate_inode(inode);
> > struct hugepage_subpool *spool = subpool_inode(inode);
> > struct resv_map *resv_map;
> > + struct hugetlb_cgroup *h_cg;
> > long gbl_reserve;
> >
> > /* This should never happen */
> > @@ -4534,12 +4561,30 @@ int hugetlb_reserve_pages(struct inode *inode,
> > chg = region_chg(resv_map, from, to);
> >
> > } else {
> > + /* Private mapping. */
> > resv_map = resv_map_alloc();
> > if (!resv_map)
> > return -ENOMEM;
> >
> > chg = to - from;
> >
> > + if (hugetlb_cgroup_charge_cgroup(hstate_index(h),
> > + chg * pages_per_huge_page(h),
> > + &h_cg, true)) {
> > + kref_put(&resv_map->refs, resv_map_release);
> > + return -ENOMEM;
> > + }
> > +
>
> Shouldn't this code be in the #ifdef CONFIG_CGROUP_HUGETLB block?

Not necessary AFAICT, hugetlb_cgroup_charge_cgroup stub returns 0 (no-op).

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