Re: [PATCH v4 2/2] arm64: mm: hugetlb: Enable HUGETLB_PAGE_FREE_VMEMMAP for arm64

[Anshuman Khandual]

Hello Muchun,

On 3/31/22 12:26, Muchun Song wrote:
> The feature of minimizing overhead of struct page associated with each
> HugeTLB page aims to free its vmemmap pages (used as struct page) to
> save memory, where is ~14GB/16GB per 1TB HugeTLB pages (2MB/1GB type).

Enabling this feature saves us around 1.4/1.6 % memory but looking from
other way around, unavailability of vmemmap backing pages (~1.4GB) when
freeing up a corresponding HugeTLB page, could prevent ~1TB memory from
being used as normal page form (requiring their own struct pages), thus
forcing the HugeTLB page to remain as such ? Is not this problematic ?

These additional 1TB memory in normal pages, from a HugeTLB dissolution
could have eased the system's memory pressure without this feature being
enabled.

- Anshuman