linux-kernel - Re: [PATCH RFC 3/3] ARM: reduce size of page table directory for short mode

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Message-ID: <20141118230255.GA3841@e104818-lin.cambridge.arm.com>
Date:	Tue, 18 Nov 2014 23:02:55 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Konstantin Khlebnikov <k.khlebnikov@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH RFC 3/3] ARM: reduce size of page table directory for
 short mode

On Tue, Nov 18, 2014 at 07:11:04PM +0000, Russell King - ARM Linux wrote:
> On Tue, Nov 18, 2014 at 06:14:12PM +0000, Catalin Marinas wrote:
> > Actually, with LPAE you can save a pmd and pte allocated for the vectors
> > page at 0xffff0000. So you can save 8K per task here. Similarly with the
> > classic MMU, you can save another 4K for the vectors page pte.
> 
> No.  For any CPU which has high vectors (approximately ARMv5 and up),
> there is no "vectors page pte".  The vectors page PTE is only allocated
> when we need low vectors.

You are right. The kernel pgd entries are copied by pgd_alloc, so no
need for additional pmd/pte allocations (they would be shared).

-- 
Catalin
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