This makes CMA memory area size zero for x86 in default configuration (doesn't change on the other architectures). If default CMA size is zero, DMA_CMA is disabled. It can be enabled by passing cma= to the kernel.
This makes less impact on x86. Because there is no mainline driver that requires it for x86, and Peter Hurley reported the performance regression, as this is trying to drive _all_ dma mapping allocations through a _very_ small window. Signed-off-by: Akinobu Mita <[email protected]> Reported-by: Peter Hurley <[email protected]> Cc: Peter Hurley <[email protected]> Cc: Chuck Ebbert <[email protected]> Cc: Jean Delvare <[email protected]> Cc: Marek Szyprowski <[email protected]> Cc: Konrad Rzeszutek Wilk <[email protected]> Cc: David Woodhouse <[email protected]> Cc: Don Dutile <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Yinghai Lu <[email protected]> Cc: [email protected] Cc: [email protected] --- * v2 - Add information in help text, suggested by Chuck Ebbert drivers/base/Kconfig | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig index 4e7f0ff..115882f 100644 --- a/drivers/base/Kconfig +++ b/drivers/base/Kconfig @@ -240,18 +240,24 @@ comment "Default contiguous memory area size:" config CMA_SIZE_MBYTES int "Size in Mega Bytes" depends on !CMA_SIZE_SEL_PERCENTAGE + default 0 if X86 default 16 help Defines the size (in MiB) of the default memory area for Contiguous - Memory Allocator. + Memory Allocator. If the size of 0 is selected, CMA is disabled by + default, but it can be enabled by passing cma=size[MG] to the kernel. + config CMA_SIZE_PERCENTAGE int "Percentage of total memory" depends on !CMA_SIZE_SEL_MBYTES + default 0 if X86 default 10 help Defines the size of the default memory area for Contiguous Memory Allocator as a percentage of the total memory in the system. + If 0 percent is selected, CMA is disabled by default, but it can be + enabled by passing cma=size[MG] to the kernel. choice prompt "Selected region size" -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
