From: Andrew Morton <akpm@linux-foundation.org>
To: Brian Geffon <bgeffon@google.com>
Cc: "Michael S . Tsirkin" <mst@redhat.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-api@vger.kernel.org, Andy Lutomirski <luto@amacapital.net>,
Will Deacon <will@kernel.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Sonny Rao <sonnyrao@google.com>, Minchan Kim <minchan@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Yu Zhao <yuzhao@google.com>, Jesse Barnes <jsbarnes@google.com>,
Nathan Chancellor <natechancellor@gmail.com>,
Florian Weimer <fweimer@redhat.com>,
"Kirill A . Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH v4] mm: Add MREMAP_DONTUNMAP to mremap().
Date: Sun, 9 Feb 2020 17:21:40 -0800 [thread overview]
Message-ID: <20200209172140.aa60488e10e0408c4f74f11b@linux-foundation.org> (raw)
In-Reply-To: <20200207201856.46070-1-bgeffon@google.com>
On Fri, 7 Feb 2020 12:18:56 -0800 Brian Geffon <bgeffon@google.com> wrote:
> When remapping an anonymous, private mapping, if MREMAP_DONTUNMAP is
> set, the source mapping will not be removed. Instead it will be
> cleared as if a brand new anonymous, private mapping had been created
> atomically as part of the mremap() call. If a userfaultfd was watching
> the source, it will continue to watch the new mapping. For a mapping
> that is shared or not anonymous, MREMAP_DONTUNMAP will cause the
> mremap() call to fail. Because MREMAP_DONTUNMAP always results in moving
> a VMA you MUST use the MREMAP_MAYMOVE flag. The final result is two
> equally sized VMAs where the destination contains the PTEs of the source.
>
> We hope to use this in Chrome OS where with userfaultfd we could write
> an anonymous mapping to disk without having to STOP the process or worry
> about VMA permission changes.
>
> This feature also has a use case in Android, Lokesh Gidra has said
> that "As part of using userfaultfd for GC, We'll have to move the physical
> pages of the java heap to a separate location. For this purpose mremap
> will be used. Without the MREMAP_DONTUNMAP flag, when I mremap the java
> heap, its virtual mapping will be removed as well. Therefore, we'll
> require performing mmap immediately after. This is not only time consuming
> but also opens a time window where a native thread may call mmap and
> reserve the java heap's address range for its own usage. This flag
> solves the problem."
This seems useful and reasonably mature, so I'll queue it for
additional testing and shall await review feedback.
Could we please get some self-test code for this feature in
tools/testing/selftests/vm? Perhaps in userfaultfd.c?
next prev parent reply other threads:[~2020-02-10 1:21 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-07 20:18 [PATCH v4] mm: Add MREMAP_DONTUNMAP to mremap() Brian Geffon
2020-02-07 20:21 ` [PATCH] mremap.2: Add information for MREMAP_DONTUNMAP Brian Geffon
2020-02-13 12:55 ` Christian Brauner
2020-02-10 1:21 ` Andrew Morton [this message]
2020-02-10 18:38 ` [PATCH v4] mm: Add MREMAP_DONTUNMAP to mremap() Brian Geffon
2020-02-10 10:45 ` Kirill A. Shutemov
2020-02-10 14:12 ` Brian Geffon
2020-02-13 12:08 ` Kirill A. Shutemov
2020-02-13 18:20 ` Brian Geffon
2020-02-14 0:36 ` Kirill A. Shutemov
2020-02-11 23:13 ` Daniel Colascione
2020-02-11 23:32 ` Brian Geffon
2020-02-11 23:53 ` Daniel Colascione
2020-02-14 4:09 ` [PATCH v5 1/2] " Brian Geffon
2020-02-14 4:09 ` [PATCH v5 2/2] selftest: Add MREMAP_DONTUNMAP selftest Brian Geffon
2020-02-14 14:28 ` [PATCH v5 1/2] mm: Add MREMAP_DONTUNMAP to mremap() Kirill A. Shutemov
2020-02-14 18:46 ` Brian Geffon
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