On Mon, 16 Mar 2015, Tomasz Figa wrote:
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 83cd5ac..f081e9e 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -1145,18 +1145,31 @@ static struct page **__iommu_alloc_buffer(struct
> device *dev, size_t size,
> }
>
> /*
> - * IOMMU can map any pages, so himem can also be used here
> + * IOMMU can map any pages, so himem can also be used here.
> + * We do not want OOM killer to be invoked as long as we can fall back
> + * to single pages, so we use __GFP_NORETRY for positive orders.
> */
> - gfp |= __GFP_NOWARN | __GFP_HIGHMEM;
> + gfp |= __GFP_NOWARN | __GFP_HIGHMEM | __GFP_NORETRY;
>
> while (count) {
> - int j, order = __fls(count);
> + int j, order;
>
> - pages[i] = alloc_pages(gfp, order);
> - while (!pages[i] && order)
> - pages[i] = alloc_pages(gfp, --order);
> - if (!pages[i])
> - goto error;
> + for (order = __fls(count); order; --order) {
> + /* Will not trigger OOM. */
> + pages[i] = alloc_pages(gfp, order);
> + if (pages[i])
> + break;
> + }
> +
> + if (!pages[i]) {
> + /*
> + * Fall back to single page allocation.
> + * Might invoke OOM killer as last resort.
> + */
> + pages[i] = alloc_pages(gfp & ~__GFP_NORETRY, 0);
> + if (!pages[i])
> + goto error;
> + }
>
> if (order) {
> split_page(pages[i], order);
I think this makes sense, but the problem is the unconditional setting and
clearing of __GFP_NORETRY. Strictly speaking, gfp may already have
__GFP_NORETRY set when calling this function so it would be better to do
the loop with alloc_pages(gfp | __GFP_NORETRY, order) and then the
fallback as alloc_page(gfp).
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