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Date: Wed, 13 Oct 2010 17:23:43 -0700 From: "H. Peter Anvin" <hpa@...or.com> To: David Rientjes <rientjes@...gle.com> CC: Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Casey Dahlin <cdahlin@...hat.com>, x86@...nel.org, linux-kernel@...r.kernel.org Subject: Re: [patch] x86: allow ZONE_DMA to be configurable 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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