Re: [PATCH 1/2] memory tiering: read last_cpupid correctly in do_huge_pmd_numa_page()

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2024/7/19 22:43, Zi Yan wrote:
> last_cpupid is only available when memory tiering is off or the folio
> is in toptier node. Complete the check to read last_cpupid when it is
> available.
> 
> Before the fix, the default last_cpupid will be used even if memory
> tiering mode is turned off at runtime instead of the actual value. This
> can prevent task_numa_fault() from getting right numa fault stats, but
> should not cause any crash. User might see performance changes after the
> fix.
> 
> Reported-by: David Hildenbrand <david@redhat.com>
> Closes: https://lore.kernel.org/linux-mm/9af34a6b-ca56-4a64-8aa6-ade65f109288@redhat.com/
> Fixes: 33024536bafd ("memory tiering: hot page selection with hint page fault latency")
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Acked-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>

and we better to check numabalance mode in migrate_misplaced_folio()?

--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2630,7 +2630,8 @@ int migrate_misplaced_folio(struct folio *folio, 
struct vm_area_struct *vma,
                 putback_movable_pages(&migratepages);
         if (nr_succeeded) {
                 count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded);
-               if (!node_is_toptier(folio_nid(folio)) && 
node_is_toptier(node))
+               if ((sysctl_numa_balancing_mode & 
NUMA_BALANCING_MEMORY_TIERING)
+                   &&!node_is_toptier(folio_nid(folio)) && 
node_is_toptier(node))
                         mod_node_page_state(pgdat, PGPROMOTE_SUCCESS,
                                             nr_succeeded);
         }



> ---
>   mm/huge_memory.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index f4be468e06a4..825317aee88e 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1712,7 +1712,8 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
>   	 * For memory tiering mode, cpupid of slow memory page is used
>   	 * to record page access time.  So use default value.
>   	 */
> -	if (node_is_toptier(nid))
> +	if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) ||
> +	    node_is_toptier(nid))
>   		last_cpupid = folio_last_cpupid(folio);
>   	target_nid = numa_migrate_prep(folio, vmf, haddr, nid, &flags);
>   	if (target_nid == NUMA_NO_NODE)