iommu/iova: Retry from last rb tree node if iova search fails
When ever a new iova alloc request comes iova is always searched from the cached node and the nodes which are previous to cached node. So, even if there is free iova space available in the nodes which are next to the cached node iova allocation can still fail because of this approach. Consider the following sequence of iova alloc and frees on 1GB of iova space 1) alloc - 500MB 2) alloc - 12MB 3) alloc - 499MB 4) free - 12MB which was allocated in step 2 5) alloc - 13MB After the above sequence we will have 12MB of free iova space and cached node will be pointing to the iova pfn of last alloc of 13MB which will be the lowest iova pfn of that iova space. Now if we get an alloc request of 2MB we just search from cached node and then look for lower iova pfn's for free iova and as they aren't any, iova alloc fails though there is 12MB of free iova space. To avoid such iova search failures do a retry from the last rb tree node when iova search fails, this will search the entire tree and get an iova if its available. Signed-off-by: Vijayanand Jitta <vjitta@codeaurora.org> Reviewed-by: Robin Murphy <robin.murphy@arm.com> Link: https://lore.kernel.org/r/1601451864-5956-1-git-send-email-vjitta@codeaurora.orgSigned-off-by: Will Deacon <will@kernel.org>
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