Re: [PATCH v2 00/19] mm: Support huge pfnmaps

[Peter Xu <peterx@redhat.com>]

On Tue, Aug 27, 2024 at 03:36:07PM -0700, Jiaqi Yan wrote:
> Hi Peter,

Hi, Jiaqi,

> I am curious if there is any work needed for unmap_mapping_range? If a
> driver hugely remap_pfn_range()ed at 1G granularity, can the driver
> unmap at PAGE_SIZE granularity? For example, when handling a PFN is

Yes it can, but it'll invoke the split_huge_pud() which default routes to
removal of the whole pud right now (currently only covers either DAX
mappings or huge pfnmaps; it won't for anonymous if it comes, for example).

In that case it'll rely on the driver providing proper fault() /
huge_fault() to refault things back with smaller sizes later when accessed
again.

> poisoned in the 1G mapping, it would be great if the mapping can be
> splitted to 2M mappings + 4k mappings, so only the single poisoned PFN
> is lost. (Pretty much like the past proposal* to use HGM** to improve
> hugetlb's memory failure handling).

Note that we're only talking about MMIO mappings here, in which case the
PFN doesn't even have a struct page, so the whole poison idea shouldn't
apply, afaiu.

Thanks,

-- 
Peter Xu