From: Rik van Riel <riel@surriel.com>
To: Matthew Wilcox <willy@infradead.org>, Andy Lutomirski <luto@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>,
Anton Blanchard <anton@ozlabs.org>, Arnd Bergmann <arnd@arndb.de>,
linux-arch <linux-arch@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
X86 ML <x86@kernel.org>, Will Deacon <will@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Dave Hansen <dave.hansen@intel.com>
Subject: Re: [MOCKUP] x86/mm: Lightweight lazy mm refcounting
Date: Thu, 03 Dec 2020 09:26:32 -0500 [thread overview]
Message-ID: <0239dde7da2d6b6499970f343c7498c711ce14c2.camel@surriel.com> (raw)
In-Reply-To: <20201203123129.GH11935@casper.infradead.org>
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On Thu, 2020-12-03 at 12:31 +0000, Matthew Wilcox wrote:
> And this just makes me think RCU freeing of mm_struct. I'm sure it's
> more complicated than that (then, or now), but if an anonymous
> process
> is borrowing a freed mm, and the mm is freed by RCU then it will not
> go
> away until the task context switches. When we context switch back to
> the anon task, it'll borrow some other task's MM and won't even
> notice
> that the MM it was using has gone away.
One major complication here is that most of the
active_mm borrowing is done by the idle task,
but RCU does not wait for idle tasks to context
switch.
That means RCU, as it is today, is not a
mechanism that mm_struct freeing could just
piggyback off.
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prev parent reply other threads:[~2020-12-03 14:47 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-03 5:25 Andy Lutomirski
2020-12-03 7:11 ` kernel test robot
2020-12-03 8:44 ` Peter Zijlstra
2020-12-03 22:13 ` Nicholas Piggin
2020-12-04 2:17 ` Andy Lutomirski
2020-12-03 12:31 ` Matthew Wilcox
2020-12-03 14:26 ` Rik van Riel [this message]
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