Messages in this thread | | | From | David Howells <> | Subject | Re: [PATCH v7 0/8] iov_iter: Improve page extraction (ref, pin or just list) | Date | Mon, 23 Jan 2023 16:38:47 +0000 |
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Matthew Wilcox <willy@infradead.org> wrote:
> Why do we want to track that information on a per-page basis? Wouldn't it > be easier to have a VM_NOCOW flag in vma->vm_flags? Set it the first > time somebody does an O_DIRECT read or RDMA pin. That's it. Pages in > that VMA will now never be COWed, regardless of their refcount/mapcount. > And the whole "did we pin or get this page" problem goes away. Along > with folio->pincount.
Wouldn't that potentially make someone's entire malloc() heap entirely NOCOW if they did a single DIO to/from it.
Also you only mention DIO read - but what about "start DIO write; fork(); touch buffer" in the parent - now the write buffer belongs to the child and they can affect the parent's write.
David
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