Re: [PATCH v5 1/4] mm: add per-order mTHP anon_fault_alloc and anon_fault_fallback counters

[Barry Song <21cnbao@gmail.com>]

On Fri, Apr 12, 2024 at 9:27 PM Ryan Roberts <ryan.roberts@arm.com> wrote:
>
> Hi Barry,
>
> 2 remaining comments - otherwise looks good. (same comments I just made in the
> v4 conversation).
>
> On 12/04/2024 08:37, Barry Song wrote:
> > From: Barry Song <v-songbaohua@oppo.com>
> >
> > Profiling a system blindly with mTHP has become challenging due to the
> > lack of visibility into its operations.  Presenting the success rate of
> > mTHP allocations appears to be pressing need.
> >
> > Recently, I've been experiencing significant difficulty debugging
> > performance improvements and regressions without these figures.  It's
> > crucial for us to understand the true effectiveness of mTHP in real-world
> > scenarios, especially in systems with fragmented memory.
> >
> > This patch establishes the framework for per-order mTHP
> > counters. It begins by introducing the anon_fault_alloc and
> > anon_fault_fallback counters. Additionally, to maintain consistency
> > with thp_fault_fallback_charge in /proc/vmstat, this patch also tracks
> > anon_fault_fallback_charge when mem_cgroup_charge fails for mTHP.
> > Incorporating additional counters should now be straightforward as well.
> >
> > Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> > Cc: Chris Li <chrisl@kernel.org>
> > Cc: David Hildenbrand <david@redhat.com>
> > Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
> > Cc: Kairui Song <kasong@tencent.com>
> > Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> > Cc: Peter Xu <peterx@redhat.com>
> > Cc: Ryan Roberts <ryan.roberts@arm.com>
> > Cc: Suren Baghdasaryan <surenb@google.com>
> > Cc: Yosry Ahmed <yosryahmed@google.com>
> > Cc: Yu Zhao <yuzhao@google.com>
> > ---
> >  include/linux/huge_mm.h | 51 ++++++++++++++++++++++++++++++++++
> >  mm/huge_memory.c        | 61 +++++++++++++++++++++++++++++++++++++++++
> >  mm/memory.c             |  3 ++
> >  mm/page_alloc.c         |  4 +++
> >  4 files changed, 119 insertions(+)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index e896ca4760f6..c5beb54b97cb 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -264,6 +264,57 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
> >                                         enforce_sysfs, orders);
> >  }
> >
> > +enum mthp_stat_item {
> > +     MTHP_STAT_ANON_FAULT_ALLOC,
> > +     MTHP_STAT_ANON_FAULT_FALLBACK,
> > +     MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
> > +     __MTHP_STAT_COUNT
> > +};
> > +
> > +struct mthp_stat {
> > +     unsigned long stats[0][__MTHP_STAT_COUNT];
> > +};
> > +
> > +extern struct mthp_stat __percpu *mthp_stats;
> > +
> > +static inline void count_mthp_stat(int order, enum mthp_stat_item item)
> > +{
> > +     if (order <= 0 || order > PMD_ORDER || !mthp_stats)
> > +             return;
> > +
> > +     this_cpu_inc(mthp_stats->stats[order][item]);
> > +}
> > +
> > +static inline void count_mthp_stats(int order, enum mthp_stat_item item, long delta)
> > +{
> > +     if (order <= 0 || order > PMD_ORDER || !mthp_stats)
> > +             return;
> > +
> > +     this_cpu_add(mthp_stats->stats[order][item], delta);
> > +}
> > +
> > +/*
> > + * Fold the foreign cpu mthp stats into our own.
> > + *
> > + * This is adding to the stats on one processor
> > + * but keeps the global counts constant.
> > + */
> > +static inline void mthp_stats_fold_cpu(int cpu)
> > +{
> > +     struct mthp_stat *fold_stat;
> > +     int i, j;
> > +
> > +     if (!mthp_stats)
> > +             return;
> > +     fold_stat = per_cpu_ptr(mthp_stats, cpu);
> > +     for (i = 1; i <= PMD_ORDER; i++) {
> > +             for (j = 0; j < __MTHP_STAT_COUNT; j++) {
> > +                     count_mthp_stats(i, j, fold_stat->stats[i][j]);
> > +                     fold_stat->stats[i][j] = 0;
> > +             }
> > +     }
> > +}
>
> This is a pretty horrible hack; I'm pretty sure just summing for all *possible*
> cpus should work.
>
> > +
> >  #define transparent_hugepage_use_zero_page()                         \
> >       (transparent_hugepage_flags &                                   \
> >        (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG))
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index dc30139590e6..21c4ac74b484 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -526,6 +526,50 @@ static const struct kobj_type thpsize_ktype = {
> >       .sysfs_ops = &kobj_sysfs_ops,
> >  };
> >
> > +struct mthp_stat __percpu *mthp_stats;
> > +
> > +static unsigned long sum_mthp_stat(int order, enum mthp_stat_item item)
> > +{
> > +     unsigned long sum = 0;
> > +     int cpu;
> > +
> > +     cpus_read_lock();
> > +     for_each_online_cpu(cpu) {
> > +             struct mthp_stat *this = per_cpu_ptr(mthp_stats, cpu);
> > +
> > +             sum += this->stats[order][item];
> > +     }
> > +     cpus_read_unlock();
> > +
> > +     return sum;
> > +}
> > +
> > +#define DEFINE_MTHP_STAT_ATTR(_name, _index)                                 \
> > +static ssize_t _name##_show(struct kobject *kobj,                    \
> > +                     struct kobj_attribute *attr, char *buf)         \
> > +{                                                                    \
> > +     int order = to_thpsize(kobj)->order;                            \
> > +                                                                     \
> > +     return sysfs_emit(buf, "%lu\n", sum_mthp_stat(order, _index));  \
> > +}                                                                    \
> > +static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> > +
> > +DEFINE_MTHP_STAT_ATTR(anon_fault_alloc, MTHP_STAT_ANON_FAULT_ALLOC);
> > +DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK);
> > +DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
> > +
> > +static struct attribute *stats_attrs[] = {
> > +     &anon_fault_alloc_attr.attr,
> > +     &anon_fault_fallback_attr.attr,
> > +     &anon_fault_fallback_charge_attr.attr,
> > +     NULL,
> > +};
> > +
> > +static struct attribute_group stats_attr_group = {
> > +     .name = "stats",
> > +     .attrs = stats_attrs,
> > +};
> > +
> >  static struct thpsize *thpsize_create(int order, struct kobject *parent)
> >  {
> >       unsigned long size = (PAGE_SIZE << order) / SZ_1K;
> > @@ -549,6 +593,12 @@ static struct thpsize *thpsize_create(int order, struct kobject *parent)
> >               return ERR_PTR(ret);
> >       }
> >
> > +     ret = sysfs_create_group(&thpsize->kobj, &stats_attr_group);
> > +     if (ret) {
> > +             kobject_put(&thpsize->kobj);
> > +             return ERR_PTR(ret);
> > +     }
> > +
> >       thpsize->order = order;
> >       return thpsize;
> >  }
> > @@ -691,6 +741,11 @@ static int __init hugepage_init(void)
> >        */
> >       MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER < 2);
> >
> > +     mthp_stats = __alloc_percpu((PMD_ORDER + 1) * sizeof(mthp_stats->stats[0]),
> > +                     sizeof(unsigned long));
>
> Personally I think it would be cleaner to allocate statically using
> ilog2(MAX_PTRS_PER_PTE) instead of PMD_ORDER.

Hi Ryan,

I don't understand why MAX_PTRS_PER_PTE is the correct size. For ARM64,

#define PMD_ORDER       (PMD_SHIFT - PAGE_SHIFT)

#define MAX_PTRS_PER_PTE PTRS_PER_PTE

#define PTRS_PER_PTE            (1 << (PAGE_SHIFT - 3))

while PAGE_SIZE is 16KiB or 64KiB, PTRS_PER_PTE can be a huge number?


Am I missing something?

>
> > +     if (!mthp_stats)
> > +             return -ENOMEM;
> > +
> >       err = hugepage_init_sysfs(&hugepage_kobj);
> >       if (err)
> >               goto err_sysfs;
> > @@ -725,6 +780,8 @@ static int __init hugepage_init(void)
> >  err_slab:
> >       hugepage_exit_sysfs(hugepage_kobj);
> >  err_sysfs:
> > +     free_percpu(mthp_stats);
> > +     mthp_stats = NULL;
> >       return err;
> >  }
> >  subsys_initcall(hugepage_init);
> > @@ -880,6 +937,8 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
> >               folio_put(folio);
> >               count_vm_event(THP_FAULT_FALLBACK);
> >               count_vm_event(THP_FAULT_FALLBACK_CHARGE);
> > +             count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK);
> > +             count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
> >               return VM_FAULT_FALLBACK;
> >       }
> >       folio_throttle_swaprate(folio, gfp);
> > @@ -929,6 +988,7 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
> >               mm_inc_nr_ptes(vma->vm_mm);
> >               spin_unlock(vmf->ptl);
> >               count_vm_event(THP_FAULT_ALLOC);
> > +             count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_ALLOC);
> >               count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
> >       }
> >
> > @@ -1050,6 +1110,7 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
> >       folio = vma_alloc_folio(gfp, HPAGE_PMD_ORDER, vma, haddr, true);
> >       if (unlikely(!folio)) {
> >               count_vm_event(THP_FAULT_FALLBACK);
> > +             count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK);
> >               return VM_FAULT_FALLBACK;
> >       }
> >       return __do_huge_pmd_anonymous_page(vmf, &folio->page, gfp);
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 649a547fe8e3..06048af7cf9a 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -4368,6 +4368,7 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
> >               folio = vma_alloc_folio(gfp, order, vma, addr, true);
> >               if (folio) {
> >                       if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
> > +                             count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
> >                               folio_put(folio);
> >                               goto next;
> >                       }
> > @@ -4376,6 +4377,7 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
> >                       return folio;
> >               }
> >  next:
> > +             count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
> >               order = next_order(&orders, order);
> >       }
> >
> > @@ -4485,6 +4487,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
> >
> >       folio_ref_add(folio, nr_pages - 1);
> >       add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages);
> > +     count_mthp_stat(folio_order(folio), MTHP_STAT_ANON_FAULT_ALLOC);
> >       folio_add_new_anon_rmap(folio, vma, addr);
> >       folio_add_lru_vma(folio, vma);
> >  setpte:
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index b51becf03d1e..3135b5ca2457 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5840,6 +5840,10 @@ static int page_alloc_cpu_dead(unsigned int cpu)
> >        */
> >       vm_events_fold_cpu(cpu);
> >
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +     mthp_stats_fold_cpu(cpu);
> > +#endif
> > +
> >       /*
> >        * Zero the differential counters of the dead processor
> >        * so that the vm statistics are consistent.
>