Messages in this thread | | | Date | Thu, 26 Mar 2015 10:01:46 +0530 | Subject | Re: [PATCH v2] ARM: mm: Do not invoke OOM for higher order IOMMU DMA allocations | From | Ritesh Harjani <> |
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On Thu, Mar 26, 2015 at 6:04 AM, David Rientjes <rientjes@google.com> wrote: > On Thu, 26 Mar 2015, Ritesh Harjani wrote: > >> > diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c >> > index 83cd5ac..3f1ac51 100644 >> > --- a/arch/arm/mm/dma-mapping.c >> > +++ b/arch/arm/mm/dma-mapping.c >> > @@ -1150,13 +1150,28 @@ static struct page **__iommu_alloc_buffer(struct device *dev, size_t size, >> > gfp |= __GFP_NOWARN | __GFP_HIGHMEM; >> > >> > while (count) { >> > - int j, order = __fls(count); >> > + int j, order; >> > + >> > + for (order = __fls(count); order > 0; --order) { >> > + /* >> > + * We do not want OOM killer to be invoked as long >> > + * as we can fall back to single pages, so we force >> > + * __GFP_NORETRY for orders higher than zero. >> > + */ >> > + pages[i] = alloc_pages(gfp | __GFP_NORETRY, order); >> > + if (pages[i]) >> > + break; >> > + } >> > >> > - pages[i] = alloc_pages(gfp, order); >> > - while (!pages[i] && order) >> > - pages[i] = alloc_pages(gfp, --order); >> > - if (!pages[i]) >> > - goto error; >> > + if (!pages[i]) { >> > + /* >> > + * Fall back to single page allocation. >> > + * Might invoke OOM killer as last resort. >> > + */ >> > + pages[i] = alloc_pages(gfp, 0); >> I think down the code in this while loop, i & count is being >> calculated based on the "order" of allocation in the current >> iteration. >> Since value of order will be automatically 0 here if (!pages[i]) is >> true then, why hard code order to value of 0 here. >> Comment clearly says what this code is doing right? >> > > Gcc is smart enough to know that order == 0 here, the code generation on > arm will be the same, so this is only a matter of how the source looks.
Agreed. > To me, it doesn't make a lot of sense to write it as alloc_pages(gfp, > order) when order is always equal to 0. I think it's clearer the way that > Tomasz wrote it.
Ok > >> I know it is just a minor thing. Don't know if it is relevant. >> >> > + if (!pages[i]) >> > + goto error; >> > + } >> > >> > if (order) { >> > split_page(pages[i], order);
Thanks Ritesh
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