From: Hugh Dickins <hughd@google.com>
To: Alistair Popple <apopple@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Axel Rasmussen <axelrasmussen@google.com>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Miaohe Lin <linmiaohe@huawei.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
Jerome Glisse <jglisse@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Nadav Amit <nadav.amit@gmail.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v3 04/27] mm/userfaultfd: Introduce special pte for unmapped file-backed mem
Date: Thu, 3 Jun 2021 20:14:31 -0700 (PDT) [thread overview]
Message-ID: <alpine.LSU.2.11.2106031954570.12760@eggly.anvils> (raw)
In-Reply-To: <1780227.rxkhHXaqZV@nvdebian>
On Fri, 4 Jun 2021, Alistair Popple wrote:
>
> The detail which is perhaps less important is whether to implement this using
> a new swap entry type or arch-specific swap bit. The argument for using a swap
> type is it will work across architectures due to the use of pte_to_swp_entry()
> and swp_entry_to_pte() to convert to and from the arch-dependent and
> independent representations.
>
> The argument against seems to have been that it is wasting a swap type.
> However if I'm understanding correctly that's not true for all architectures,
> and needing to reserve a bit is more wasteful than using a swap type.
I'm on the outside, not paying much attention here,
but thought Peter would have cleared this up already.
My understanding is that it does *not* use an additional arch-dependent
bit, but puts the _PAGE_UFFD_WP bit (already set aside by any architecture
implementing UFFD WP) to an additional use. That's why I called this
design (from Andrea) more elegant than mine (swap type business).
If I've got that wrong, and yet another arch-dependent bit is needed,
then I very much agree with you: finding arch-dependent pte bits is a
much tougher job than another play with swap type.
(And "more elegant" might not be "easier to understand": you decide.)
Hugh
next prev parent reply other threads:[~2021-06-04 3:14 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-27 20:19 [PATCH v3 00/27] userfaultfd-wp: Support shmem and hugetlbfs Peter Xu
2021-05-27 20:19 ` [PATCH v3 01/27] mm/shmem: Unconditionally set pte dirty in mfill_atomic_install_pte Peter Xu
2021-05-27 20:19 ` [PATCH v3 02/27] shmem/userfaultfd: Take care of UFFDIO_COPY_MODE_WP Peter Xu
2021-05-27 20:19 ` [PATCH v3 03/27] mm: Clear vmf->pte after pte_unmap_same() returns Peter Xu
2021-05-27 20:19 ` [PATCH v3 04/27] mm/userfaultfd: Introduce special pte for unmapped file-backed mem Peter Xu
2021-05-28 8:32 ` Alistair Popple
2021-05-28 12:56 ` Peter Xu
2021-06-03 11:53 ` Alistair Popple
2021-06-03 14:51 ` Peter Xu
2021-06-04 0:55 ` Alistair Popple
2021-06-04 3:14 ` Hugh Dickins [this message]
2021-06-04 6:16 ` Alistair Popple
2021-06-04 16:01 ` Peter Xu
2021-06-08 13:18 ` Alistair Popple
2021-06-09 13:06 ` Alistair Popple
2021-06-09 14:43 ` Peter Xu
2021-05-27 20:21 ` [PATCH v3 05/27] mm/swap: Introduce the idea of special swap ptes Peter Xu
2021-05-27 20:21 ` [PATCH v3 06/27] shmem/userfaultfd: Handle uffd-wp special pte in page fault handler Peter Xu
2021-06-17 8:59 ` Alistair Popple
2021-06-17 15:10 ` Peter Xu
2021-05-27 20:21 ` [PATCH v3 07/27] mm: Drop first_index/last_index in zap_details Peter Xu
2021-06-21 12:20 ` Alistair Popple
2021-05-27 20:21 ` [PATCH v3 08/27] mm: Introduce zap_details.zap_flags Peter Xu
2021-06-21 12:09 ` Alistair Popple
2021-06-21 16:16 ` Peter Xu
2021-06-22 2:07 ` Alistair Popple
2021-05-27 20:21 ` [PATCH v3 09/27] mm: Introduce ZAP_FLAG_SKIP_SWAP Peter Xu
2021-06-21 12:36 ` Alistair Popple
2021-06-21 16:26 ` Peter Xu
2021-06-22 2:11 ` Alistair Popple
2021-05-27 20:21 ` [PATCH v3 10/27] mm: Pass zap_flags into unmap_mapping_pages() Peter Xu
2021-05-27 20:22 ` [PATCH v3 11/27] shmem/userfaultfd: Persist uffd-wp bit across zapping for file-backed Peter Xu
2021-06-21 8:41 ` Alistair Popple
2021-06-22 0:40 ` Peter Xu
2021-06-22 12:47 ` Alistair Popple
2021-06-22 15:44 ` Peter Xu
2021-06-23 6:04 ` Alistair Popple
2021-06-23 15:31 ` Peter Xu
2021-07-06 5:40 ` Alistair Popple
2021-07-06 15:35 ` Peter Xu
2021-07-08 2:49 ` Alistair Popple
2021-05-27 20:22 ` [PATCH v3 12/27] shmem/userfaultfd: Allow wr-protect none pte for file-backed mem Peter Xu
2021-05-27 20:22 ` [PATCH v3 13/27] shmem/userfaultfd: Allows file-back mem to be uffd wr-protected on thps Peter Xu
2021-05-27 20:22 ` [PATCH v3 14/27] shmem/userfaultfd: Handle the left-overed special swap ptes Peter Xu
2021-05-27 20:22 ` [PATCH v3 15/27] shmem/userfaultfd: Pass over uffd-wp special swap pte when fork() Peter Xu
2021-05-27 20:23 ` [PATCH v3 16/27] mm/hugetlb: Drop __unmap_hugepage_range definition from hugetlb.h Peter Xu
2021-05-27 20:23 ` [PATCH v3 17/27] mm/hugetlb: Introduce huge pte version of uffd-wp helpers Peter Xu
2021-05-27 20:23 ` [PATCH v3 18/27] hugetlb/userfaultfd: Hook page faults for uffd write protection Peter Xu
2021-05-27 20:23 ` [PATCH v3 19/27] hugetlb/userfaultfd: Take care of UFFDIO_COPY_MODE_WP Peter Xu
2021-05-27 20:23 ` [PATCH v3 20/27] hugetlb/userfaultfd: Handle UFFDIO_WRITEPROTECT Peter Xu
2021-05-27 20:23 ` [PATCH v3 21/27] mm/hugetlb: Introduce huge version of special swap pte helpers Peter Xu
2021-05-27 20:23 ` [PATCH v3 22/27] hugetlb/userfaultfd: Handle uffd-wp special pte in hugetlb pf handler Peter Xu
2021-05-27 20:23 ` [PATCH v3 23/27] hugetlb/userfaultfd: Allow wr-protect none ptes Peter Xu
2021-05-27 20:23 ` [PATCH v3 24/27] hugetlb/userfaultfd: Only drop uffd-wp special pte if required Peter Xu
2021-05-27 20:23 ` [PATCH v3 25/27] mm/pagemap: Recognize uffd-wp bit for shmem/hugetlbfs Peter Xu
2021-05-27 20:23 ` [PATCH v3 26/27] mm/userfaultfd: Enable write protection for shmem & hugetlbfs Peter Xu
2021-05-27 20:23 ` [PATCH v3 27/27] userfaultfd/selftests: Enable uffd-wp for shmem/hugetlbfs Peter Xu
2021-06-02 14:40 ` [PATCH v3 00/27] userfaultfd-wp: Support shmem and hugetlbfs Peter Xu
2021-06-02 22:36 ` Andrew Morton
2021-06-03 0:09 ` Peter Xu
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