Commit e8b19840 authored Sep 28, 2017 by Robin Murphy Committed by Joerg Roedel Sep 28, 2017

iommu/iova: Try harder to allocate from rcache magazine

When devices with different DMA masks are using the same domain, or for
PCI devices where we usually try a speculative 32-bit allocation first,
there is a fair possibility that the top PFN of the rcache stack at any
given time may be unsuitable for the lower limit, prompting a fallback
to allocating anew from the rbtree. Consequently, we may end up
artifically increasing pressure on the 32-bit IOVA space as unused IOVAs
accumulate lower down in the rcache stacks, while callers with 32-bit
masks also impose unnecessary rbtree overhead.

In such cases, let's try a bit harder to satisfy the allocation locally
first - scanning the whole stack should still be relatively inexpensive.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

parent b826ee9a

drivers/iommu/iova.c

+12 −3

Original line number	Diff line number	Diff line
		@@ -821,12 +821,21 @@ static bool iova_magazine_empty(struct iova_magazine *mag)
		static unsigned long iova_magazine_pop(struct iova_magazine *mag,
		unsigned long limit_pfn)
		{
		int i;
		unsigned long pfn;

		BUG_ON(iova_magazine_empty(mag));

		if (mag->pfns[mag->size - 1] > limit_pfn)
		/* Only fall back to the rbtree if we have no suitable pfns at all */
		for (i = mag->size - 1; mag->pfns[i] > limit_pfn; i--)
		if (i == 0)
		return 0;

		return mag->pfns[--mag->size];
		/* Swap it to pop it */
		pfn = mag->pfns[i];
		mag->pfns[i] = mag->pfns[--mag->size];

		return pfn;
		}

		static void iova_magazine_push(struct iova_magazine *mag, unsigned long pfn)