From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Brian Geffon <bgeffon@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
"Michael S . Tsirkin" <mst@redhat.com>,
Arnd Bergmann <arnd@arndb.de>,
LKML <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>
Subject: Re: [PATCH v4] mm: Add MREMAP_DONTUNMAP to mremap().
Date: Fri, 14 Feb 2020 03:36:40 +0300 [thread overview]
Message-ID: <20200214003640.yphbnjw7omsx2rje@box> (raw)
In-Reply-To: <CADyq12wWOhGDeUeOB74dxuRKjPhduMWZLBMxOxpm5-yHOpjaRw@mail.gmail.com>
On Thu, Feb 13, 2020 at 10:20:44AM -0800, Brian Geffon wrote:
> Hi Kirill,
>
> > But if you do the operation for the VM_LOCKED vma, you'll have two locked
> > VMA's now, right? Where do you account the old locked vma you left behind?
>
> You bring up a good point. In a previous iteration of my patch I had
> it clearing the locked flags on the old VMA as technically the locked
> pages had migrated. I talked myself out of that but the more I think
> about it we should probably do that. Something along the lines of:
>
> + if (vm_flags & VM_LOCKED) {
> + /* Locked pages would have migrated to the new VMA */
> + vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
> + if (new_len > old_len)
> + mm->locked_vm += (new_len - old_len) >> PAGE_SHIFT;
> + }
>
> I feel that this is correct. The only other possible option would be
> to clear only the VM_LOCKED flag on the old vma leaving VM_LOCKONFAULT
> to handle the MCL_ONFAULT mlocked situation, thoughts? Regardless I'll
> have to mail a new patch because that part where I'm incrementing the
> mm->locked_vm lost the check on VM_LOCKED during patch versions.
Note, that we account mlock limit on per-VMA basis, not per page. Even for
VM_LOCKONFAULT.
> Thanks again for taking the time to review.
I believe the right approach is to strip VM_LOCKED[ONFAULT] from the vma
you left behind. Or the new vma. It is a policy decision.
JFYI, we do not inherit VM_LOCKED on fork(), so it's common practice to
strip VM_LOCKED on vma duplication.
Other option is to leave VM_LOCKED on both VMAs and fail the operation if
we are over the limit. But we need to have a good reason to take this
path. It makes the interface less flexible.
--
Kirill A. Shutemov
next prev parent reply other threads:[~2020-02-14 0:36 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 [this message]
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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