From: Peter Xu <peterx@redhat.com>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mina Almasry <almasrymina@google.com>,
Linux-MM <linux-mm@kvack.org>,
Axel Rasmussen <axelrasmussen@google.com>,
aarcange@redhat.com
Subject: Re: resv_huge_page underflow with userfaultfd test
Date: Tue, 11 May 2021 22:35:10 -0400 [thread overview]
Message-ID: <YJs+3orgxYdVfwD+@t490s> (raw)
In-Reply-To: <096e28e2-5937-beb2-57f7-d112f9b54d97@oracle.com>
Mike,
On Tue, May 11, 2021 at 07:25:39PM -0700, Mike Kravetz wrote:
> I looked at this a bit more today and am not exactly sure of the
> expected behavior. The situation is:
> - UFFDIO_COPY is called for hugetlb mapping
> - the dest address is in a shared mapping
> - there is a page in the cache associated with the address in the
> shared mapping
>
> Currently, the code will fail when trying to update the page cache as
> the entry already exists. The shm code appears to do the same.
>
> Quick question. Is this the expected behavior? Or, would you expect
> the UFFDIO_COPY to update the page in the page cache, and then resolve
> the fault/update the pte?
AFAICT that's the expected behavior, and it need to be like that so as to avoid
silent data corruption (if the page cache existed, it means the page is not
"missing" at all, then it does not suite for a UFFDIO_COPY as it's only used
for uffd page missing case). Thanks,
--
Peter Xu
next prev parent reply other threads:[~2021-05-12 2:35 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-07 21:21 resv_huge_page underflow with userfaultfd test Mina Almasry
2021-05-11 0:33 ` Mike Kravetz
2021-05-11 0:52 ` Mina Almasry
2021-05-11 6:45 ` Axel Rasmussen
2021-05-11 7:08 ` Mina Almasry
2021-05-11 16:38 ` Mike Kravetz
2021-05-11 19:08 ` Mina Almasry
2021-05-12 2:25 ` Mike Kravetz
2021-05-12 2:35 ` Peter Xu [this message]
2021-05-12 3:06 ` Mike Kravetz
[not found] ` <20210512065813.89270-1-almasrymina@google.com>
2021-05-12 7:44 ` [PATCH] mm, hugetlb: fix resv_huge_pages underflow on UFFDIO_COPY Mina Almasry
[not found] ` <CAJHvVch0ZMapPVEc0Ge5V4KDgNDNhECbqwDi0y9XxsxFXQZ-gg@mail.gmail.com>
[not found] ` <c455d241-11f6-95a6-eb29-0ddd94eedbd7@oracle.com>
2021-05-12 19:42 ` Mina Almasry
2021-05-12 20:14 ` Peter Xu
2021-05-12 21:31 ` Mike Kravetz
2021-05-12 21:52 ` Mina Almasry
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