[PATCH 3/3] iommu/dma: Avoid unlikely high-order allocations

[Doug Anderson]

Robin,

On Fri, Dec 18, 2015 at 9:01 AM, Robin Murphy <robin.murphy at arm.com> wrote:
> Doug reports that the equivalent page allocator on 32-bit ARM exhibits
> particularly pathalogical behaviour under memory pressure when
> fragmentation is high, where allocating a 4MB buffer takes tens of
> seconds and the number of calls to alloc_pages() is over 9000![1]
>
> We can drastically improve that situation without losing the other
> benefits of high-order allocations when they would succeed, by assuming
> memory pressure is relatively constant over the course of an allocation,
> and not retrying allocations at orders we know to have failed before.
> This way, the best-case behaviour remains unchanged, and in the worst
> case we should see at most a dozen or so (MAX_ORDER - 1) failed attempts
> before falling back to single pages for the remainder of the buffer.
>
> [1]:http://lists.infradead.org/pipermail/linux-arm-kernel/2015-December/394660.html
>
> Reported-by: Douglas Anderson <dianders at chromium.org>
> Signed-off-by: Robin Murphy <robin.murphy at arm.com>
> ---
>  drivers/iommu/dma-iommu.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)

Presumably it makes sense to update this based on v2 of my patch to
the original code?  AKA: <https://patchwork.kernel.org/patch/7888851/>
?