Re: [RFC PATCH 2/3] mm/memory-tiers: Use page counter to track toptier memory usage

[Wei Xu <weixugc@google.com>]

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On Tue, Jun 14, 2022 at 3:26 PM Tim Chen <tim.c.chen@linux.intel.com> wrote:

> If we need to restrict toptier memory usage for a cgroup,
> we need to retrieve usage of toptier memory efficiently.
> Add a page counter to track toptier memory usage directly
> so its value can be returned right away.
> ---
>  include/linux/memcontrol.h |  1 +
>  mm/memcontrol.c            | 50 ++++++++++++++++++++++++++++++++------
>  2 files changed, 43 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 9ecead1042b9..b4f727cba1de 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -241,6 +241,7 @@ struct mem_cgroup {
>
>         /* Accounted resources */
>         struct page_counter memory;             /* Both v1 & v2 */
> +       struct page_counter toptier;
>
>         union {
>                 struct page_counter swap;       /* v2 only */
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2f6e95e6d200..2f20ec2712b8 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -848,6 +848,23 @@ static void mem_cgroup_charge_statistics(struct
> mem_cgroup *memcg,
>         __this_cpu_add(memcg->vmstats_percpu->nr_page_events, nr_pages);
>  }
>
> +static inline void mem_cgroup_charge_toptier(struct mem_cgroup *memcg,
> +                                            int nid,
> +                                            int nr_pages)
> +{
> +       if (!node_is_toptier(nid) || !memcg)
> +               return;
> +
> +       if (nr_pages >= 0) {
> +               page_counter_charge(&memcg->toptier,
> +                               (unsigned long) nr_pages);
> +       } else {
> +               nr_pages = -nr_pages;
> +               page_counter_uncharge(&memcg->toptier,
> +                               (unsigned long) nr_pages);
> +       }
> +}
> +
>

When we don't know which pages are being charged, we should still charge
the usage to toptier (assuming that toptier always include the default
tier), e.g. from try_charge_memcg().

The idea is that when lower tier memory is not used, memcg->toptier and
memcg->memory should have the same value. Otherwise, it can cause
confusions about where the pages of (memcg->memory - memcg->toptier) go.

 static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
>                                        enum mem_cgroup_events_target
> target)
>  {
> @@ -3027,6 +3044,8 @@ int __memcg_kmem_charge_page(struct page *page,
> gfp_t gfp, int order)
>                 if (!ret) {
>                         page->memcg_data = (unsigned long)objcg |
>                                 MEMCG_DATA_KMEM;
> +                       mem_cgroup_charge_toptier(page_memcg(page),
> +                                       page_to_nid(page), 1 << order);
>                         return 0;
>                 }
>                 obj_cgroup_put(objcg);
> @@ -3050,6 +3069,8 @@ void __memcg_kmem_uncharge_page(struct page *page,
> int order)
>
>         objcg = __folio_objcg(folio);
>         obj_cgroup_uncharge_pages(objcg, nr_pages);
> +       mem_cgroup_charge_toptier(page_memcg(page),
> +                       page_to_nid(page), -nr_pages);
>         folio->memcg_data = 0;
>         obj_cgroup_put(objcg);
>  }
> @@ -3947,13 +3968,10 @@ unsigned long mem_cgroup_memtier_usage(struct
> mem_cgroup *memcg,
>
>  unsigned long mem_cgroup_toptier_usage(struct mem_cgroup *memcg)
>  {
> -       struct memory_tier *top_tier;
> -
> -       top_tier = list_first_entry(&memory_tiers, struct memory_tier,
> list);
> -       if (top_tier)
> -               return mem_cgroup_memtier_usage(memcg, top_tier);
> -       else
> +       if (!memcg)
>                 return 0;
> +
> +       return page_counter_read(&memcg->toptier);
>  }
>
>  #endif /* CONFIG_NUMA */
> @@ -5228,11 +5246,13 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state
> *parent_css)
>                 memcg->oom_kill_disable = parent->oom_kill_disable;
>
>                 page_counter_init(&memcg->memory, &parent->memory);
> +               page_counter_init(&memcg->toptier, &parent->toptier);
>                 page_counter_init(&memcg->swap, &parent->swap);
>                 page_counter_init(&memcg->kmem, &parent->kmem);
>                 page_counter_init(&memcg->tcpmem, &parent->tcpmem);
>         } else {
>                 page_counter_init(&memcg->memory, NULL);
> +               page_counter_init(&memcg->toptier, NULL);
>                 page_counter_init(&memcg->swap, NULL);
>                 page_counter_init(&memcg->kmem, NULL);
>                 page_counter_init(&memcg->tcpmem, NULL);
> @@ -5678,6 +5698,8 @@ static int mem_cgroup_move_account(struct page *page,
>         memcg_check_events(to, nid);
>         mem_cgroup_charge_statistics(from, -nr_pages);
>         memcg_check_events(from, nid);
> +       mem_cgroup_charge_toptier(to, nid, nr_pages);
> +       mem_cgroup_charge_toptier(from, nid, -nr_pages);
>         local_irq_enable();
>  out_unlock:
>         folio_unlock(folio);
> @@ -6761,6 +6783,7 @@ static int charge_memcg(struct folio *folio, struct
> mem_cgroup *memcg,
>
>         local_irq_disable();
>         mem_cgroup_charge_statistics(memcg, nr_pages);
> +       mem_cgroup_charge_toptier(memcg, folio_nid(folio), nr_pages);
>         memcg_check_events(memcg, folio_nid(folio));
>         local_irq_enable();
>  out:
> @@ -6853,6 +6876,7 @@ struct uncharge_gather {
>         unsigned long nr_memory;
>         unsigned long pgpgout;
>         unsigned long nr_kmem;
> +       unsigned long nr_toptier;
>         int nid;
>  };
>
> @@ -6867,6 +6891,7 @@ static void uncharge_batch(const struct
> uncharge_gather *ug)
>
>         if (ug->nr_memory) {
>                 page_counter_uncharge(&ug->memcg->memory, ug->nr_memory);
> +               page_counter_uncharge(&ug->memcg->toptier, ug->nr_toptier);
>                 if (do_memsw_account())
>                         page_counter_uncharge(&ug->memcg->memsw,
> ug->nr_memory);
>                 if (ug->nr_kmem)
> @@ -6929,12 +6954,18 @@ static void uncharge_folio(struct folio *folio,
> struct uncharge_gather *ug)
>                 ug->nr_memory += nr_pages;
>                 ug->nr_kmem += nr_pages;
>
> +               if (node_is_toptier(folio_nid(folio)))
> +                       ug->nr_toptier += nr_pages;
> +
>                 folio->memcg_data = 0;
>                 obj_cgroup_put(objcg);
>         } else {
>                 /* LRU pages aren't accounted at the root level */
> -               if (!mem_cgroup_is_root(memcg))
> +               if (!mem_cgroup_is_root(memcg)) {
>                         ug->nr_memory += nr_pages;
> +                       if (node_is_toptier(folio_nid(folio)))
> +                               ug->nr_toptier += nr_pages;
> +               }
>                 ug->pgpgout++;
>
>                 folio->memcg_data = 0;
> @@ -7011,6 +7042,7 @@ void mem_cgroup_migrate(struct folio *old, struct
> folio *new)
>         /* Force-charge the new page. The old one will be freed soon */
>         if (!mem_cgroup_is_root(memcg)) {
>                 page_counter_charge(&memcg->memory, nr_pages);
> +               mem_cgroup_charge_toptier(memcg, folio_nid(new), nr_pages);
>                 if (do_memsw_account())
>                         page_counter_charge(&memcg->memsw, nr_pages);
>         }
> @@ -7231,8 +7263,10 @@ void mem_cgroup_swapout(struct folio *folio,
> swp_entry_t entry)
>
>         folio->memcg_data = 0;
>
> -       if (!mem_cgroup_is_root(memcg))
> +       if (!mem_cgroup_is_root(memcg)) {
>                 page_counter_uncharge(&memcg->memory, nr_entries);
> +               mem_cgroup_charge_toptier(memcg, folio_nid(folio),
> -nr_entries);
> +       }
>
>         if (!cgroup_memory_noswap && memcg != swap_memcg) {
>                 if (!mem_cgroup_is_root(swap_memcg))
> --
> 2.35.1
>
>
>

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