From: Hugh Dickins <hughd@google.com>
To: Axel Rasmussen <axelrasmussen@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Andrea Arcangeli <aarcange@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
Jerome Glisse <jglisse@redhat.com>, Joe Perches <joe@perches.com>,
Lokesh Gidra <lokeshgidra@google.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
Peter Xu <peterx@redhat.com>, Shaohua Li <shli@fb.com>,
Shuah Khan <shuah@kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Wang Qing <wangqing@vivo.com>,
linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-mm@kvack.org, Brian Geffon <bgeffon@google.com>,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
Mina Almasry <almasrymina@google.com>,
Oliver Upton <oupton@google.com>
Subject: Re: [PATCH v5 04/10] userfaultfd/shmem: support UFFDIO_CONTINUE for shmem
Date: Tue, 27 Apr 2021 17:03:17 -0700 (PDT) [thread overview]
Message-ID: <alpine.LSU.2.11.2104271702470.7111@eggly.anvils> (raw)
In-Reply-To: <20210427225244.4326-5-axelrasmussen@google.com>
On Tue, 27 Apr 2021, Axel Rasmussen wrote:
> With this change, userspace can resolve a minor fault within a
> shmem-backed area with a UFFDIO_CONTINUE ioctl. The semantics for this
> match those for hugetlbfs - we look up the existing page in the page
> cache, and install a PTE for it.
>
> This commit introduces a new helper: mcopy_atomic_install_pte.
>
> Why handle UFFDIO_CONTINUE for shmem in mm/userfaultfd.c, instead of in
> shmem.c? The existing userfault implementation only relies on shmem.c
> for VM_SHARED VMAs. However, minor fault handling / CONTINUE work just
> fine for !VM_SHARED VMAs as well. We'd prefer to handle CONTINUE for
> shmem in one place, regardless of shared/private (to reduce code
> duplication).
>
> Why add a new mcopy_atomic_install_pte helper? A problem we have with
> continue is that shmem_mcopy_atomic_pte() and mcopy_atomic_pte() are
> *close* to what we want, but not exactly. We do want to setup the PTEs
> in a CONTINUE operation, but we don't want to e.g. allocate a new page,
> charge it (e.g. to the shmem inode), manipulate various flags, etc. Also
> we have the problem stated above: shmem_mcopy_atomic_pte() and
> mcopy_atomic_pte() both handle one-half of the problem (shared /
> private) continue cares about. So, introduce mcontinue_atomic_pte(), to
> handle all of the shmem continue cases. Introduce the helper so it
> doesn't duplicate code with mcopy_atomic_pte().
>
> In a future commit, shmem_mcopy_atomic_pte() will also be modified to
> use this new helper. However, since this is a bigger refactor, it seems
> most clear to do it as a separate change.
>
> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
> ---
> mm/userfaultfd.c | 172 ++++++++++++++++++++++++++++++++++-------------
> 1 file changed, 127 insertions(+), 45 deletions(-)
next prev parent reply other threads:[~2021-04-28 0:03 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-27 22:52 [PATCH v5 00/10] userfaultfd: add minor fault handling for shmem Axel Rasmussen
2021-04-27 22:52 ` [PATCH v5 01/10] userfaultfd/hugetlbfs: avoid including userfaultfd_k.h in hugetlb.h Axel Rasmussen
2021-04-27 22:52 ` [PATCH v5 02/10] userfaultfd/shmem: combine shmem_{mcopy_atomic,mfill_zeropage}_pte Axel Rasmussen
2021-04-27 22:52 ` [PATCH v5 03/10] userfaultfd/shmem: support minor fault registration for shmem Axel Rasmussen
2021-04-28 0:02 ` Hugh Dickins
2021-04-27 22:52 ` [PATCH v5 04/10] userfaultfd/shmem: support UFFDIO_CONTINUE " Axel Rasmussen
2021-04-28 0:03 ` Hugh Dickins [this message]
2021-04-28 15:10 ` Peter Xu
2021-04-27 22:52 ` [PATCH v5 05/10] userfaultfd/shmem: advertise shmem minor fault support Axel Rasmussen
2021-04-28 0:04 ` Hugh Dickins
2021-04-28 15:11 ` Peter Xu
2021-04-27 22:52 ` [PATCH v5 06/10] userfaultfd/shmem: modify shmem_mcopy_atomic_pte to use install_pte() Axel Rasmussen
2021-04-28 0:58 ` Hugh Dickins
2021-04-28 15:56 ` Peter Xu
2021-04-28 15:59 ` Axel Rasmussen
2021-04-28 16:23 ` Peter Xu
2021-04-27 22:52 ` [PATCH v5 07/10] userfaultfd/selftests: use memfd_create for shmem test type Axel Rasmussen
2021-04-27 22:52 ` [PATCH v5 08/10] userfaultfd/selftests: create alias mappings in the shmem test Axel Rasmussen
2021-04-27 22:52 ` [PATCH v5 09/10] userfaultfd/selftests: reinitialize test context in each test Axel Rasmussen
2021-04-28 17:23 ` Peter Xu
2021-05-18 20:57 ` Peter Xu
2021-05-18 22:28 ` Axel Rasmussen
2021-04-27 22:52 ` [PATCH v5 10/10] userfaultfd/selftests: exercise minor fault handling shmem support Axel Rasmussen
2021-04-28 17:26 ` Peter Xu
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