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

["Huang, Ying" <ying.huang@intel.com>]

Yang Shi <shy828301@gmail.com> writes:

> 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?

PGPROMOTE_SUCCESS is a per-node counter. That is, its type is enum
node_stat_item instead of enum vm_event_item.  So we need to use
mod_node_page_state() instead of count_vm_events().  The new API is to
avoid #ifdef CONFIG_NUMA_BALANCING/#endif in caller.

Best Regards,
Huang, Ying

>>  #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
>>