Re: [PATCH RFC v2 02/18] mm: add pghint_t type and vma_alloc_folio_hints API

[Huang, Ying]

"Michael S. Tsirkin" <mst@xxxxxxxxxx> writes:

> Add pghint_t, a bitwise type for communicating page allocation hints
> between the allocator and callers.  Define PGHINT_ZEROED to indicate
> that the allocated page contents are known to be zero.
>
> Add _hints variants of the allocation functions that accept a
> pghint_t *hints output parameter:
>
>   vma_alloc_folio_hints()  -> folio_alloc_mpol_hints (internal)
>                            -> __alloc_frozen_pages_hints()
>
> The existing APIs are unchanged and continue to work without hints.
> For now, hints is always initialized to 0.  A subsequent patch will
> set PGHINT_ZEROED when the page was pre-zeroed by the host.

Why do we need this feature?  Is there any performance impact?  If so,
please provide some performance data.

[snip]

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Best Regards,
Huang, Ying