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From: "Martin J. Bligh" <mbligh@mbligh.org>
To: Hugh Dickins <hugh@veritas.com>, Arjan van de Ven <arjan@infradead.org>
Cc: Dave McCracken <dmccr@us.ibm.com>, Andrew Morton <akpm@osdl.org>,
	Linux Kernel <linux-kernel@vger.kernel.org>,
	Linux Memory Management <linux-mm@kvack.org>
Subject: Re: [PATCH 1/1] Implement shared page tables
Date: Wed, 31 Aug 2005 07:31:52 -0700	[thread overview]
Message-ID: <16640000.1125498711@[10.10.2.4]> (raw)
In-Reply-To: <Pine.LNX.4.61.0508311437070.16834@goblin.wat.veritas.com>

--Hugh Dickins <hugh@veritas.com> wrote (on Wednesday, August 31, 2005 14:42:38 +0100):

> On Wed, 31 Aug 2005, Arjan van de Ven wrote:
>> On Wed, 2005-08-31 at 12:44 +0100, Hugh Dickins wrote:
>> > I was going to say, doesn't randomize_va_space take away the rest of
>> > the point?  But no, it appears "randomize_va_space", as it currently
>> > appears in mainline anyway, is somewhat an exaggeration: it just shifts
>> > the stack a little, with no effect on the rest of the va space.
>> 
>> it also randomizes mmaps
> 
> Ah, via PF_RANDOMIZE, yes, thanks: so long as certain conditions are
> fulfilled - and my RLIM_INFINITY RLIMIT_STACK has been preventing it.
> 
> And mmaps include shmats: so unless the process specifies non-NULL
> shmaddr to attach at, it'll choose a randomized address for that too
> (subject to those various conditions).
> 
> Which is indeed a further disincentive against shared page tables.

Or shared pagetables a disincentive to randomizing the mmap space ;-)
They're incompatible, but you could be left to choose one or the other
via config option.

3% on "a certain industry-standard database benchmark" (cough) is huge,
and we expect the benefit for PPC64 will be larger as we can share the
underlying hardware PTEs without TLB flushing as well.

M.


  reply	other threads:[~2005-08-31 14:32 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-08-30 22:13 [PATCH 1/1] Implement shared page tables Dave McCracken
2005-08-31 11:44 ` Hugh Dickins
2005-08-31 11:51   ` Arjan van de Ven
2005-08-31 13:42     ` Hugh Dickins
2005-08-31 14:31       ` Martin J. Bligh [this message]
2005-08-31 14:41         ` Arjan van de Ven
2005-08-31 15:06         ` Hugh Dickins
2005-08-31 15:39           ` Martin J. Bligh
2005-08-31 16:40   ` Dave McCracken
2005-09-02  1:58 ` Chen, Kenneth W
2005-09-02 16:40   ` Dave McCracken
2005-09-02  4:26 ` Chen, Kenneth W

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