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Commit dc382fd5bcca7098a984705ed6ac880f539d068e

Authored by David Rientjes
Committed by H. Peter Anvin
1 parent e5a10c1bd1
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

x86, mm: Allow ZONE_DMA to be configurable 

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>

Showing 3 changed files with 12 additions and 1 deletions Side-by-side Diff

... ... @@ -112,7 +112,14 @@
112 112 def_bool y
113 113  
114 114 config ZONE_DMA
115   - def_bool y
  115 + bool "DMA memory allocation support" if EXPERT
  116 + default y
  117 + help
  118 + DMA memory allocation support allows devices with less than 32-bit
  119 + addressing to allocate within the first 16MB of address space.
  120 + Disable if no such devices will be used.
  121 +
  122 + If unsure, say Y.
116 123  
117 124 config SBUS
118 125 bool
arch/x86/mm/init_32.c
Diff comments   View file @ dc382fd
... ... @@ -678,8 +678,10 @@
678 678 {
679 679 unsigned long max_zone_pfns[MAX_NR_ZONES];
680 680 memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
  681 +#ifdef CONFIG_ZONE_DMA
681 682 max_zone_pfns[ZONE_DMA] =
682 683 virt_to_phys((char *)MAX_DMA_ADDRESS) >> PAGE_SHIFT;
  684 +#endif
683 685 max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
684 686 #ifdef CONFIG_HIGHMEM
685 687 max_zone_pfns[ZONE_HIGHMEM] = highend_pfn;
arch/x86/mm/init_64.c
Diff comments   View file @ dc382fd
... ... @@ -616,7 +616,9 @@
616 616 unsigned long max_zone_pfns[MAX_NR_ZONES];
617 617  
618 618 memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
  619 +#ifdef CONFIG_ZONE_DMA
619 620 max_zone_pfns[ZONE_DMA] = MAX_DMA_PFN;
  621 +#endif
620 622 max_zone_pfns[ZONE_DMA32] = MAX_DMA32_PFN;
621 623 max_zone_pfns[ZONE_NORMAL] = max_pfn;
622 624