Messages in this thread Patch in this message | | | Date | Wed, 27 Apr 2011 16:37:48 -0700 (PDT) | From | David Rientjes <> | Subject | [patch v3] x86: allow ZONE_DMA to be configurable |
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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 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.
Signed-off-by: David Rientjes <rientjes@google.com> --- v3: did s/old ISA devices/devices/ as suggested by H. Peter Anvin.
arch/x86/Kconfig | 9 ++++++++- arch/x86/mm/init_32.c | 2 ++ arch/x86/mm/init_64.c | 2 ++ 3 files changed, 12 insertions(+), 1 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -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 16-bit address + registers to allocate memory within the first 16MB of address space. + Disable if no such devices will be used. + + If unsure, say Y. config SBUS bool diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c --- a/arch/x86/mm/init_32.c +++ b/arch/x86/mm/init_32.c @@ -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; diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -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;
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