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
