linux-kernel - Re: [RFC PATCHv3 00/11] Intermix Lowmem and vmalloc

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Date:	Sat, 4 Jan 2014 07:31:43 +0000
From:	Minchan Kim <minchan@...nel.org>
To:	Laura Abbott <lauraa@...eaurora.org>
Cc:	Dave Hansen <dave@...1.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kyungmin Park <kmpark@...radead.org>, linux-mm@...ck.org,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCHv3 00/11] Intermix Lowmem and vmalloc

Hello,

On Fri, Jan 03, 2014 at 02:08:52PM -0800, Laura Abbott wrote:
> On 1/3/2014 10:23 AM, Dave Hansen wrote:
> >On 01/02/2014 01:53 PM, Laura Abbott wrote:
> >>The goal here is to allow as much lowmem to be mapped as if the block of memory
> >>was not reserved from the physical lowmem region. Previously, we had been
> >>hacking up the direct virt <-> phys translation to ignore a large region of
> >>memory. This did not scale for multiple holes of memory however.
> >
> >How much lowmem do these holes end up eating up in practice, ballpark?
> >I'm curious how painful this is going to get.
> >
> 
> In total, the worst case can be close to 100M with an average case
> around 70M-80M. The split and number of holes vary with the layout
> but end up with 60M-80M one hole and the rest in the other.

One more thing I'd like to know is how bad direct virt <->phys tranlsation
in scale POV and how often virt<->phys tranlsation is called in your worload
so what's the gain from this patch?

Thanks.

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