If CONFIG_DMA_CMA is enabled, dma_generic_alloc_coherent() tries to allocate memory region by dma_alloc_from_contiguous() before trying to use alloc_pages().
This wastes CMA region by small DMA-coherent buffers which can be allocated by alloc_pages(). And it also causes performance degradation, as this is trying to drive _all_ dma mapping allocations through a _very_ small window, reported by Peter Hurley. This fixes it by trying to allocate by alloc_pages() first in dma_generic_alloc_coherent() as dma_alloc_from_contiguous should be called only for huge allocation. Signed-off-by: Akinobu Mita <[email protected]> Reported-by: Peter Hurley <[email protected]> Cc: Peter Hurley <[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] --- arch/x86/kernel/pci-dma.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c index a25e202..0402266 100644 --- a/arch/x86/kernel/pci-dma.c +++ b/arch/x86/kernel/pci-dma.c @@ -99,20 +99,20 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size, flag &= ~__GFP_ZERO; again: - page = NULL; + page = alloc_pages_node(dev_to_node(dev), flag | __GFP_NOWARN, + get_order(size)); /* CMA can be used only in the context which permits sleeping */ - if (flag & __GFP_WAIT) { + if (!page && (flag & __GFP_WAIT)) { page = dma_alloc_from_contiguous(dev, count, get_order(size)); if (page && page_to_phys(page) + size > dma_mask) { dma_release_from_contiguous(dev, page, count); page = NULL; } } - /* fallback */ - if (!page) - page = alloc_pages_node(dev_to_node(dev), flag, get_order(size)); - if (!page) + if (!page) { + warn_alloc_failed(flag, get_order(size), NULL); return NULL; + } addr = page_to_phys(page); if (addr + size > dma_mask) { -- 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/
