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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>
This commit is contained in:
Robin Murphy 2017-09-28 11:31:23 +01:00 committed by Joerg Roedel
parent b826ee9a4f
commit e8b1984027
1 changed files with 12 additions and 3 deletions
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15
drivers/iommu/iova.c
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@ -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)
return 0;
/* 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)