On 29.11.24 13:26, Peter Zijlstra wrote:
On Fri, Nov 29, 2024 at 01:12:57PM +0100, David Hildenbrand wrote:
Well, I think we simply will want vm_insert_pages_prot() that stops treating
these things like folios :) . *likely* we'd want a distinct memdesc/type.
We could start that work right now by making some user (iouring,
ring_buffer) set a new page->_type, and checking that in
vm_insert_pages_prot() + vm_normal_page(). If set, don't touch the refcount
and the mapcount.
Because then, we can just make all the relevant drivers set the type, refuse
in vm_insert_pages_prot() anything that doesn't have the type set, and
refuse in vm_normal_page() any pages with this memdesc.
Maybe we'd have to teach CoW to copy from such pages, maybe not. GUP of
these things will stop working, I hope that is not a problem.
Well... perf-tool likes to call write() upon these pages in order to
write out the data from the mmap() into a file.
I think a PFNMAP as used in this patch here will already stop making
that work ....
--
Cheers,
David / dhildenb
