From: "H. Peter Anvin" <hpa@zytor.com>
To: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Casey Dahlin <cdahlin@redhat.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [patch] x86: allow ZONE_DMA to be configurable
Date: Wed, 13 Oct 2010 17:23:43 -0700 [thread overview]
Message-ID: <4CB64D8F.9080800@zytor.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1010131713160.24646@chino.kir.corp.google.com>
On 10/13/2010 05:15 PM, David Rientjes wrote:
> ZONE_DMA is unnecessary for a large number of machines that do not
> require addressing in the lower 16MB of memory because they do not use
> ISA devices with 16-bit address registers (plus one page byte register).
>
> This patch allows users to disable ZONE_DMA for x86 if they know they
> will not be using such devices with their kernel.
>
> This prevents the VM from unnecessarily reserving a ratio of memory
> (defaulting to 1/256th of system capacity) with lowmem_reserve_ratio
> for such allocations when it will never be used.
This isn't true.
There are many, many devices other than ISA devices which need access to
a restricted-memory pool because of hardware DMA limitations. This
seems like a really bad idea.
A much better idea would be to have a runtime option of setting the
reservation ratio, if recovering no more than 1/66th of a gigabyte
matters so much to you.
-hpa
next prev parent reply other threads:[~2010-10-14 0:24 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-14 0:15 [patch] x86: allow ZONE_DMA to be configurable David Rientjes
2010-10-14 0:23 ` H. Peter Anvin [this message]
2010-10-14 0:42 ` David Rientjes
2010-10-14 0:44 ` H. Peter Anvin
2010-10-14 0:49 ` David Rientjes
2010-10-14 1:21 ` H. Peter Anvin
2010-10-14 1:48 ` David Rientjes
2010-10-14 2:38 ` H. Peter Anvin
2010-10-14 3:55 ` David Rientjes
2010-10-14 4:37 ` H. Peter Anvin
2010-10-14 4:46 ` David Rientjes
2010-10-14 15:38 ` H. Peter Anvin
2010-10-14 16:00 ` Pekka Enberg
2010-10-14 17:44 ` H. Peter Anvin
2010-10-14 18:34 ` Ingo Molnar
2010-10-14 19:35 ` Andrew Morton
2010-10-14 20:40 ` H. Peter Anvin
2010-10-15 3:03 ` Ingo Molnar
2010-10-15 4:45 ` H. Peter Anvin
2010-10-15 9:05 ` David Rientjes
2010-10-15 15:06 ` H. Peter Anvin
2010-10-14 22:08 ` David Rientjes
2010-10-14 8:10 ` Andrew Morton
2010-10-14 8:32 ` KOSAKI Motohiro
2010-10-14 22:15 ` David Rientjes
2010-10-14 22:32 ` Andrew Morton
2010-10-15 3:10 ` Ingo Molnar
2010-10-15 9:11 ` David Rientjes
2010-10-15 9:09 ` David Rientjes
2010-10-21 14:56 ` Christoph Lameter
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