Re: CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is broken, was Re: [RFC PATCH 0/6] Deep talk about folio vmap

Christoph Hellwig
2025-04-07T08:59:53Z

On Mon, Apr 07, 2025 at 02:43:20PM +0800, Muchun Song wrote:
> By the way, in case you truly struggle to comprehend the fundamental
> aspects of HVO, I would like to summarize for you the user-visible
> behaviors in comparison to the situation where HVO is disabled.
>
> HVO Status Tail Page Structures Head Page Structures
> Enabled Read-Only (RO) Read-Write (RW)
> Disabled Read-Write (RW) Read-Write (RW)
>
> The sole distinction between the two scenarios lies in whether the
> tail page structures are allowed to be written or not. Please refrain
> from getting bogged down in the details of the implementation of HVO.

This feels extremely fragile to me. I doubt many people know what
operations needs read vs write access to tail pages. Or for higher
level operations if needs access to tail pages at all.