Re: [PATCH -V9 1/6] NUMA Balancing: add page promotion counter

[Yang Shi <shy828301@gmail.com>]

On Fri, Oct 8, 2021 at 1:40 AM Huang Ying <ying.huang@intel.com> wrote:
>
> In a system with multiple memory types, e.g. DRAM and PMEM, the CPU
> and DRAM in one socket will be put in one NUMA node as before, while
> the PMEM will be put in another NUMA node as described in the
> description of the commit c221c0b0308f ("device-dax: "Hotplug"
> persistent memory for use like normal RAM").  So, the NUMA balancing
> mechanism will identify all PMEM accesses as remote access and try to
> promote the PMEM pages to DRAM.
>
> To distinguish the number of the inter-type promoted pages from that
> of the inter-socket migrated pages.  A new vmstat count is added.  The
> counter is per-node (count in the target node).  So this can be used
> to identify promotion imbalance among the NUMA nodes.
>
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Rik van Riel <riel@surriel.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Yang Shi <shy828301@gmail.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Wei Xu <weixugc@google.com>
> Cc: osalvador <osalvador@suse.de>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mm@kvack.org
> ---
>  include/linux/mmzone.h |  3 +++
>  include/linux/node.h   |  5 +++++
>  include/linux/vmstat.h |  2 ++
>  mm/migrate.c           | 10 ++++++++--
>  mm/vmstat.c            |  3 +++
>  5 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 6a1d79d84675..37ccd6158765 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -209,6 +209,9 @@ enum node_stat_item {
>         NR_PAGETABLE,           /* used for pagetables */
>  #ifdef CONFIG_SWAP
>         NR_SWAPCACHE,
> +#endif
> +#ifdef CONFIG_NUMA_BALANCING
> +       PGPROMOTE_SUCCESS,      /* promote successfully */
>  #endif
>         NR_VM_NODE_STAT_ITEMS
>  };
> diff --git a/include/linux/node.h b/include/linux/node.h
> index 8e5a29897936..26e96fcc66af 100644
> --- a/include/linux/node.h
> +++ b/include/linux/node.h
> @@ -181,4 +181,9 @@ static inline void register_hugetlbfs_with_node(node_registration_func_t reg,
>
>  #define to_node(device) container_of(device, struct node, dev)
>
> +static inline bool node_is_toptier(int node)
> +{
> +       return node_state(node, N_CPU);
> +}
> +
>  #endif /* _LINUX_NODE_H_ */
> diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> index d6a6cf53b127..75c53b7d1539 100644
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -112,9 +112,11 @@ static inline void vm_events_fold_cpu(int cpu)
>  #ifdef CONFIG_NUMA_BALANCING
>  #define count_vm_numa_event(x)     count_vm_event(x)
>  #define count_vm_numa_events(x, y) count_vm_events(x, y)
> +#define mod_node_balancing_page_state(n, i, v) mod_node_page_state(n, i, v)

I don't quite get why we need this new API. Doesn't __count_vm_events() work?

>  #else
>  #define count_vm_numa_event(x) do {} while (0)
>  #define count_vm_numa_events(x, y) do { (void)(y); } while (0)
> +#define mod_node_balancing_page_state(n, i, v) do {} while (0)
>  #endif /* CONFIG_NUMA_BALANCING */
>
>  #ifdef CONFIG_DEBUG_TLBFLUSH
> diff --git a/mm/migrate.c b/mm/migrate.c
> index a6a7743ee98f..c3affc587902 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2148,6 +2148,7 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
>         pg_data_t *pgdat = NODE_DATA(node);
>         int isolated;
>         int nr_remaining;
> +       int nr_succeeded;
>         LIST_HEAD(migratepages);
>         new_page_t *new;
>         bool compound;
> @@ -2186,7 +2187,8 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
>
>         list_add(&page->lru, &migratepages);
>         nr_remaining = migrate_pages(&migratepages, *new, NULL, node,
> -                                    MIGRATE_ASYNC, MR_NUMA_MISPLACED, NULL);
> +                                    MIGRATE_ASYNC, MR_NUMA_MISPLACED,
> +                                    &nr_succeeded);
>         if (nr_remaining) {
>                 if (!list_empty(&migratepages)) {
>                         list_del(&page->lru);
> @@ -2195,8 +2197,12 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
>                         putback_lru_page(page);
>                 }
>                 isolated = 0;
> -       } else
> +       } else {
>                 count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_pages);
> +               if (!node_is_toptier(page_to_nid(page)) && node_is_toptier(node))
> +                       mod_node_balancing_page_state(
> +                               NODE_DATA(node), PGPROMOTE_SUCCESS, nr_succeeded);
> +       }
>         BUG_ON(!list_empty(&migratepages));
>         return isolated;
>
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 8ce2620344b2..fff0ec94d795 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1236,6 +1236,9 @@ const char * const vmstat_text[] = {
>  #ifdef CONFIG_SWAP
>         "nr_swapcached",
>  #endif
> +#ifdef CONFIG_NUMA_BALANCING
> +       "pgpromote_success",
> +#endif
>
>         /* enum writeback_stat_item counters */
>         "nr_dirty_threshold",
> --
> 2.30.2
>