Re: [PATCH v2 2/4] hugetlb: add HPageCma flag and code to free non-gigantic pages in CMA

[David Hildenbrand]

On 23.09.21 19:53, Mike Kravetz wrote:
> When huge page demotion is fully implemented, gigantic pages can be
> demoted to a smaller huge page size.  For example, on x86 a 1G page
> can be demoted to 512 2M pages.  However, gigantic pages can potentially
> be allocated from CMA.  If a gigantic page which was allocated from CMA
> is demoted, the corresponding demoted pages needs to be returned to CMA.
>
> In order to track hugetlb pages that need to be returned to CMA, add the
> hugetlb specific flag HPageCma.  Flag is set when a huge page is
> allocated from CMA and transferred to any demoted pages.  Non-gigantic
> huge page freeing code checks for the flag and takes appropriate action.

Do we really need that flag or couldn't we simply always try 
cma_release() and fallback to out ordinary freeing-path?

IIRC, cma knows exactly if something was allocated via a CMA are and can 
be free via it. No need for additional tracking usually.

--
Thanks,

David / dhildenb