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From: Peter Zijlstra <peterz@infradead.org>
To: Peter Oskolkov <posk@google.com>
Cc: Jann Horn <jannh@google.com>, Peter Oskolkov <posk@posk.io>,
	Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
	Paul Turner <pjt@google.com>, Ben Segall <bsegall@google.com>,
	Andrei Vagin <avagin@google.com>,
	Thierry Delisle <tdelisle@uwaterloo.ca>
Subject: Re: [PATCH 2/4 v0.5] sched/umcg: RFC: add userspace atomic helpers
Date: Tue, 14 Sep 2021 20:04:55 +0200	[thread overview]
Message-ID: <YUDkR8YtekMkuaBH@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAPNVh5chP3Zz+ww8WLb9bUYNikW-1PyOV=3==BM-92BgogaB3w@mail.gmail.com>

On Tue, Sep 14, 2021 at 09:29:00AM -0700, Peter Oskolkov wrote:
> In the version of the patchset that I'm preparing to send I've decided
> to punt on the issue and just ask the userspace to deal with locking
> the memory as it sees fit: mlock() is available and as far as I can

Sadly mlock() does not imply no faults. Someone had a too literal
reading of the POSIX-RT spec (of which mlock is part) and figured that
all that was required was to keep the page in memory, not avoid faults.

Linux has had this bahviour for ages, PREEMPT_RT has tried to change
this, but so far to no avail. At some point sys_mpin() was proposed to
meet the original POSIX-RT intent, but afaict that never actually
happened.

In short, mlock() does not avoid minor faults, or even migration faults,
which can take a fair while to resolve.

  reply	other threads:[~2021-09-14 18:05 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-08 18:49 [PATCH 0/4 v0.5] sched/umcg: RFC UMCG patchset Peter Oskolkov
2021-09-08 18:49 ` [PATCH 1/4 v0.5] sched/umcg: add WF_CURRENT_CPU and externise ttwu Peter Oskolkov
2021-09-08 18:49 ` [PATCH 2/4 v0.5] sched/umcg: RFC: add userspace atomic helpers Peter Oskolkov
2021-09-08 23:38   ` Jann Horn
2021-09-09  1:16     ` Jann Horn
2021-09-09 19:06     ` Peter Oskolkov
2021-09-09 21:20       ` Jann Horn
2021-09-09 22:09         ` Peter Oskolkov
2021-09-09 23:13           ` Jann Horn
2021-09-14 16:52         ` Andy Lutomirski
2021-09-14 18:11           ` Peter Zijlstra
2021-09-14 18:40             ` Andy Lutomirski
2021-09-15 15:42               ` Peter Zijlstra
2021-09-15 16:50                 ` Andy Lutomirski
2021-09-15 19:10                   ` Peter Zijlstra
2021-09-14  8:07       ` Peter Zijlstra
2021-09-14 16:29         ` Peter Oskolkov
2021-09-14 18:04           ` Peter Zijlstra [this message]
2021-09-14 18:15             ` Peter Zijlstra
2021-09-14 18:29             ` Peter Oskolkov
2021-09-14 18:48               ` Peter Oskolkov
2021-09-08 18:49 ` [PATCH 3/4 v0.5] sched/umcg: RFC: implement UMCG syscalls Peter Oskolkov
2021-09-08 22:02   ` kernel test robot
2021-09-09  1:39   ` Jann Horn
2021-09-14 16:51     ` Peter Oskolkov
2021-09-09 11:25   ` kernel test robot
2021-09-08 18:49 ` [PATCH 4/4 v0.5] sched/umcg: add Documentation/userspace-api/umcg.rst Peter Oskolkov
2021-09-14 16:35   ` Tao Zhou
2021-09-14 16:57     ` Peter Oskolkov

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