Re: [PATCH] mm/vmalloc: fix mischeck pfn valid in vmap_pfns

[Huan Yang]

HI Christoph

在 2025/3/18 16:44, Christoph Hellwig 写道:
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> On Tue, Mar 18, 2025 at 04:39:40PM +0800, Huan Yang wrote:
> > A folio may be 2MB or more large 1GB, what if we only need a little, 1M or 512MB, can vmap based on folio can solve it?
> Then you only map part of it by passing a length argument.  Note that
> in general when you have these large folios you also don't have highmem,
> so if you only map one of them, or part of one of them you don't actually
> need vmap at all and can just use folio-address..

The situation remains complex. We are not only referring to this single folio, but it may be composed

of multiple folios and start with a small piece. For example:

Folio 1 2M - use 1M

Folio 2 2M - use 2M

....

Combine these folios into memory used by udmabuf. So, directly virtual memory useless. :)

> > Normally, can offer 4k-page based array map it. But consider HVO, can't. That's why wanto base on pfn.
> Well, for any large folio using this 4k based page interface is
> actually highly inefficient.  So let's fix that.  And my loop in
Yes, indeed. You mentioned good to entire folio array mapped into vmalloc, I guest here are many user like it.
> willy as Mr. Folio while you're at it.
I'd like to research it, but not too fast. :)
>