From mboxrd@z Thu Jan  1 00:00:00 1970
From: arnd@arndb.de (Arnd Bergmann)
Date: Fri, 05 Dec 2014 13:24:49 +0100
Subject: [PATCH] arm64: Enable CONFIG_COMPAT also for 64k page size
In-Reply-To: <20141205110507.GB28339@e104818-lin.cambridge.arm.com>
References: <1417707993-82290-1-git-send-email-agraf@suse.de>
 <3551792.oHatG1W6W1@wuerfel>
 <20141205110507.GB28339@e104818-lin.cambridge.arm.com>
Message-ID: <2131163.V0fUaF9isN@wuerfel>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Friday 05 December 2014 11:05:07 Catalin Marinas wrote:
> 
> > Should we add support for 64k-pages in the arm32 kernel as well now?
> 
> 32-bit LPAE doesn't support 64K pages but IIRC the classic MMU does
> (though I have to check whether it was optional). But it's not feasible
> to enable this in a 32-bit environment because of the memory wasted with
> large pages (on average 32KB per mapped file, possibly even more if you
> have lots of small files).

That sounds like a tradeoff that some users might be willing to make.

I remember that with ps3-linux, a lot of people wanted to enable 64k-pages
because the Cell processor has such a small number of TLB entries (256 or
1024), but Linux only has around 200MB of memory available. I believe
there are arm32 machines with more RAM and fewer TLBs.

	Arnd