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Date: Fri, 24 Dec 2004 19:20:31 +0100
From: Andrea Arcangeli <andrea@suse.de>
To: "David S. Miller" <davem@davemloft.net>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, akpm@osdl.org
Subject: Re: VM fixes [1/4]
Message-ID: <20041224182031.GG13747@dualathlon.random>
References: <20041224173519.GB13747@dualathlon.random> <20041224100016.530a004c.davem@davemloft.net>
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On Fri, Dec 24, 2004 at 10:00:16AM -0800, David S. Miller wrote:
> On Fri, 24 Dec 2004 18:35:19 +0100
> Andrea Arcangeli <andrea@suse.de> wrote:
> 
> > I made used_math a char at the light of later patches. per-cpu atomicity
> > with byte granularity is provided by all archs AFIK.
> 
> Older Alpha's need to read-modify-write a word to implement
> byte ops.

Yep, I remeber this was the case in some old alpha. But did they support
smp too? I can't see how that old hardware could support smp. If they're
UP they're fine.

The race is extremely tiny anyway, you'd need to write to the
/proc/<pid>/ file at the same time that used_math is toggled.

Or alternatively you'd need to kill the task due oom at the same time
used_math is toggled.

The race in PF_MEMDIE is more serious.

And false sharing with memdie and oomkilladj is zero, since they're
pratically readonly.