Re: can device drivers return non-ram via vm_ops->nopage?
From: Linus Torvalds
Date: Sun Mar 21 2004 - 16:54:55 EST
On Sun, 21 Mar 2004, David Woodhouse wrote:
> On Sun, 2004-03-21 at 20:49 +0000, Christoph Hellwig wrote:
> > And what exactly is a PFN without associated struct page supposed to mean?
> It's something you can put into a PTE, and that's about it. Which unless
> I'm misunderstanding ALSA/rmk's requirements, should be enough.
It would really be wrong to have nopage() return a pte. The thing is, the
VM really works on "struct page", all over the map. It does things like
"page_cache_release()" on the page if the file-backed VMA has been
truncated, and it just knows that the return value from "nopage()" has
Some architectures have per-page flags for things like "this page may need
to have icache flushed from it" etc.
So I really put my veto on "nopage()" returning a PFN. That's just wrong,
wrong, wrong. It returns a "struct page" pointer, and it has lots of
reasons for that.
And none of the reasons for _not_ doing it are valid, since such a user
can just pre-populate the page tables anyway.
So don't go there.
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