From: Daniel Colascione <dancol@google.com>
To: Brian Geffon <bgeffon@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
"Michael S . Tsirkin" <mst@redhat.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Linux API <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: Tue, 11 Feb 2020 15:13:50 -0800 [thread overview]
Message-ID: <CAKOZuevHH1pamEKy5n5RLWDP=tHk6_9bR+g3G+HKnqm_srHvrw@mail.gmail.com> (raw)
In-Reply-To: <20200207201856.46070-1-bgeffon@google.com>
On Fri, Feb 7, 2020 at 12:19 PM 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.
The left-behind mapping (the "as if a brand new anonymous, private
mapping" map) is immediately writable, right? If so, we need to
account the additional commit charge. What about making the
left-behind mapping PROT_NONE? This way, we'll still solve the
address-space race in Lokesh's use case (because even a PROT_NONE
mapping reserves address space) but won't incur any additional commit
until someone calls mprotect(PROT_WRITE) on the left-behind mapping.
Imagine having two equal-sized mappings and wanting to use mremap() to
swap them: you can implement this swap by carving off a third region
of address space and making two mremap() calls. But without the
PROT_NONE, you pay additional commit for that third region even if you
don't need it.
next prev parent reply other threads:[~2020-02-11 23:14 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 ` [PATCH v4] mm: Add MREMAP_DONTUNMAP to mremap() Andrew Morton
2020-02-10 18:38 ` 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 [this message]
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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