On Mon, 29 Sep 2014 00:52:03 +0900 Akinobu Mita <[email protected]> wrote:
> 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)); Only try small allocs here, like when order < PAGE_ALLOC_COSTLY_ORDER ? > /* 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)); (I forgot to add this in my first reply). I think it should try for a small alloc without CMA first, then try CMA, and then this final fallback for larger allocs. > - if (!page) > + if (!page) { > + warn_alloc_failed(flag, get_order(size), NULL); > return NULL; > + } > > addr = page_to_phys(page); > if (addr + size > dma_mask) { -- 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/
