Re: [RFC PATCH 1/3] memory tiering: read last_cpupid correctly in do_huge_pmd_numa_page()

[David Hildenbrand <david@redhat.com>]

On 13.07.24 03:18, Zi Yan wrote:
> On 12 Jul 2024, at 21:13, David Hildenbrand wrote:
> 
>> On 12.07.24 04:44, Zi Yan wrote:
>>> From: Zi Yan <ziy@nvidia.com>
>>>
>>> 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.
>>>
>>> Fixes: 33024536bafd ("memory tiering: hot page selection with hint page fault latency")
>>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>>> ---
>>>    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 d7c84480f1a4..07d9dde4ca33 100644
>>> --- a/mm/huge_memory.c
>>> +++ b/mm/huge_memory.c
>>> @@ -1705,7 +1705,8 @@ 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)
>>
>> Reported-by: ...
> 
> Reported-by: David Hildenbrand <david@redhat.com>
> 
> I suppose your email[1] reports the issue based on code inspection.


Yes, thanks for taking care of the fix and cleanups!

-- 
Cheers,

David / dhildenb