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x86, mm: Allow ZONE_DMA to be configurable

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ZONE_DMA is unnecessary for a large number of machines that do not
require less than 32-bit DMA addressing, e.g. ISA legacy DMA or PCI
cards with a restricted DMA address mask.

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.

Signed-off-by: David Rientjes <rientjes@google.com>
Link: http://lkml.kernel.org/r/alpine.DEB.2.00.1105161353560.4353@chino.kir.corp.google.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
David Rientjes 2011-05-16 13:54:10 -07:00 committed by H. Peter Anvin
parent e5a10c1bd1
commit dc382fd5bc
3 changed files with 12 additions and 1 deletions
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9
arch/x86/Kconfig
View File

@ -112,7 +112,14 @@ config MMU
def_bool y
config ZONE_DMA
def_bool y
bool "DMA memory allocation support" if EXPERT
default y
help
DMA memory allocation support allows devices with less than 32-bit
addressing to allocate within the first 16MB of address space.
Disable if no such devices will be used.
If unsure, say Y.
config SBUS
bool

2
arch/x86/mm/init_32.c
View File

@ -678,8 +678,10 @@ static void __init zone_sizes_init(void)
{
unsigned long max_zone_pfns[MAX_NR_ZONES];
memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
#ifdef CONFIG_ZONE_DMA
max_zone_pfns[ZONE_DMA] =
virt_to_phys((char *)MAX_DMA_ADDRESS) >> PAGE_SHIFT;
#endif
max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
#ifdef CONFIG_HIGHMEM
max_zone_pfns[ZONE_HIGHMEM] = highend_pfn;

2
arch/x86/mm/init_64.c
View File

@ -616,7 +616,9 @@ void __init paging_init(void)
unsigned long max_zone_pfns[MAX_NR_ZONES];
memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
#ifdef CONFIG_ZONE_DMA
max_zone_pfns[ZONE_DMA] = MAX_DMA_PFN;
#endif
max_zone_pfns[ZONE_DMA32] = MAX_DMA32_PFN;
max_zone_pfns[ZONE_NORMAL] = max_pfn;