Hi David,
On Tue, Mar 17, 2015 at 8:32 AM, David Rientjes <rient...@google.com> wrote:
> 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).
Good point. I'll change it to that in next version.
Best regards,
Tomasz
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