From e8b198402745ed413ed8229b2eb45d34016eb5d8 Mon Sep 17 00:00:00 2001 From: Robin Murphy Date: Thu, 28 Sep 2017 11:31:23 +0100 Subject: [PATCH] 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 Signed-off-by: Joerg Roedel --- drivers/iommu/iova.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c index 15ff3033bbd7..b0ca23682008 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -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)