On 28-Mar-24 7:26 AM, Huang, Ying wrote:
> Bharata B Rao <bharata@xxxxxxx> writes:
>
> [snip]
>
>> @@ -1750,25 +1753,20 @@ static bool pgdat_free_space_enough(struct pglist_data *pgdat)
>> }
>>
>> /*
>> - * For memory tiering mode, when page tables are scanned, the scan
>> - * time will be recorded in struct page in addition to make page
>> - * PROT_NONE for slow memory page. So when the page is accessed, in
>> - * hint page fault handler, the hint page fault latency is calculated
>> - * via,
>> + * For memory tiering mode, when page tables are scanned, the current
>> + * hint fault count will be recorded in struct page in addition to
>> + * make page PROT_NONE for slow memory page. So when the page is
>> + * accessed, in hint page fault handler, the hint page fault latency is
>> + * calculated via,
>> *
>> - * hint page fault latency = hint page fault time - scan time
>> + * hint page fault latency = current hint fault count - fault count at scan time
>> *
>> * The smaller the hint page fault latency, the higher the possibility
>> * for the page to be hot.
>> */
>> -static int numa_hint_fault_latency(struct folio *folio)
>> +static inline int numa_hint_fault_latency(struct folio *folio, int count)
>> {
>> - int last_time, time;
>> -
>> - time = jiffies_to_msecs(jiffies);
>> - last_time = folio_xchg_access_time(folio, time);
>> -
>> - return (time - last_time) & PAGE_ACCESS_TIME_MASK;
>> + return count - folio_xchg_fault_count(folio, count);
>> }
>
> I found count is task->mm->hint_faults. That is a process wide
> counting. How do you connect the hotness of a folio with the count of
> hint page fault in the process? How do you compare the hotness of
> folios among different processes?
The global hint fault count that we already maintain could
be used instead of per-task fault. That should take care
of the concern you mention right?
Regards,
Bharata.
