Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [patch] x86: allow ZONE_DMA to be configurable | Date | Thu, 14 Oct 2010 17:32:00 +0900 (JST) |
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> On Wed, 13 Oct 2010 17:15:04 -0700 (PDT) David Rientjes <rientjes@google.com> 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. > > > > I wonder how hard it would be to do this at runtime, probably with a > boot parameter. > > I'd be a little concerned at the effects of this on page reclaim and > the page allocator - it might expose weird pre-existing bugs or > inefficiencies. But we can cross that bridge when we fall off it, I > guess.
In this case, completely ZONE disablling is not required. 16MB saving is not big matter. To prevent userland process use lower zone is necessary.
I have such patch, because 32bit highmem system has similar requirement. (user process want to only use ZONE_HIGHMEM, otherwize ZONE_NORMAL easily exshost)
I'll prepare to post them if necessary.
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