Messages in this thread | | | Date | Fri, 17 Dec 2021 20:50:41 -0400 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v1 06/11] mm: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE (!hugetlb) |
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On Fri, Dec 17, 2021 at 09:15:45PM +0000, Nadav Amit wrote:
> I think that there is an assumption that once a page is COW-broken, > it would never have another write-fault that might lead to COW > breaking later.
Yes, that is what Linus has been explaining, AFAICT
> AFAIK at least after userfaultfd-WP followed by > userfaultfd-write-unprotect a page might be write-protected and > go through do_wp_page() a second time to be COW-broken again. In > such case, I think the FOLL_FORCE|FOLL_WRITE would not help.
Right, and this is a good reason why refcount is running into trouble, it COW's too much in cases like that because userfaultfd-WP doesn't align to the first assumption.
Jason
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