Messages in this thread | | | Date | Wed, 13 Oct 2010 17:23:43 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [patch] x86: allow ZONE_DMA to be configurable |
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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
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