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

[Zi Yan <ziy@nvidia.com>]

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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.

> Closes: ...

Closes: https://lore.kernel.org/linux-mm/9af34a6b-ca56-4a64-8aa6-ade65f109288@redhat.com/

Will add them in the next version.

>
> If it applies ;)
>
> Acked-by: David Hildenbrand <david@redhat.com>

Thanks.


[1] https://lore.kernel.org/linux-mm/9af34a6b-ca56-4a64-8aa6-ade65f109288@redhat.com/

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Best Regards,
Yan, Zi

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