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Subject[RFC PATCH] iommu/iova: Add a best-fit algorithm
Date
From: Liam Mark <lmark@codeaurora.org>

Using the best-fit algorithm, instead of the first-fit
algorithm, may reduce fragmentation when allocating
IOVAs.

Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
---
drivers/iommu/dma-iommu.c | 17 +++++++++++
drivers/iommu/iova.c | 73 +++++++++++++++++++++++++++++++++++++++++++++--
include/linux/dma-iommu.h | 7 +++++
include/linux/iova.h | 1 +
4 files changed, 96 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index a2e96a5..af08770 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -364,9 +364,26 @@ static int iommu_dma_deferred_attach(struct device *dev,
if (unlikely(ops->is_attach_deferred &&
ops->is_attach_deferred(domain, dev)))
return iommu_attach_device(domain, dev);
+ return 0;
+}
+
+/*
+ * Should be called prior to using dma-apis.
+ */
+int iommu_dma_enable_best_fit_algo(struct device *dev)
+{
+ struct iommu_domain *domain;
+ struct iova_domain *iovad;
+
+ domain = iommu_get_domain_for_dev(dev);
+ if (!domain || !domain->iova_cookie)
+ return -EINVAL;

+ iovad = &((struct iommu_dma_cookie *)domain->iova_cookie)->iovad;
+ iovad->best_fit = true;
return 0;
}
+EXPORT_SYMBOL(iommu_dma_enable_best_fit_algo);

/**
* dma_info_to_prot - Translate DMA API directions and attributes to IOMMU API
diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index 0e6a953..716b05f 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -50,6 +50,7 @@ static unsigned long iova_rcache_get(struct iova_domain *iovad,
iovad->anchor.pfn_lo = iovad->anchor.pfn_hi = IOVA_ANCHOR;
rb_link_node(&iovad->anchor.node, NULL, &iovad->rbroot.rb_node);
rb_insert_color(&iovad->anchor.node, &iovad->rbroot);
+ iovad->best_fit = false;
init_iova_rcaches(iovad);
}
EXPORT_SYMBOL_GPL(init_iova_domain);
@@ -227,6 +228,69 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
return -ENOMEM;
}

+static int __alloc_and_insert_iova_best_fit(struct iova_domain *iovad,
+ unsigned long size, unsigned long limit_pfn,
+ struct iova *new, bool size_aligned)
+{
+ struct rb_node *curr, *prev;
+ struct iova *curr_iova, *prev_iova;
+ unsigned long flags;
+ unsigned long align_mask = ~0UL;
+ struct rb_node *candidate_rb_parent;
+ unsigned long new_pfn, candidate_pfn = ~0UL;
+ unsigned long gap, candidate_gap = ~0UL;
+
+ if (size_aligned)
+ align_mask <<= limit_align(iovad, fls_long(size - 1));
+
+ /* Walk the tree backwards */
+ spin_lock_irqsave(&iovad->iova_rbtree_lock, flags);
+ curr = &iovad->anchor.node;
+ prev = rb_prev(curr);
+ for (; prev; curr = prev, prev = rb_prev(curr)) {
+ curr_iova = rb_entry(curr, struct iova, node);
+ prev_iova = rb_entry(prev, struct iova, node);
+
+ limit_pfn = min(limit_pfn, curr_iova->pfn_lo);
+ new_pfn = (limit_pfn - size) & align_mask;
+ gap = curr_iova->pfn_lo - prev_iova->pfn_hi - 1;
+ if ((limit_pfn >= size) && (new_pfn > prev_iova->pfn_hi)
+ && (gap < candidate_gap)) {
+ candidate_gap = gap;
+ candidate_pfn = new_pfn;
+ candidate_rb_parent = curr;
+ if (gap == size)
+ goto insert;
+ }
+ }
+
+ curr_iova = rb_entry(curr, struct iova, node);
+ limit_pfn = min(limit_pfn, curr_iova->pfn_lo);
+ new_pfn = (limit_pfn - size) & align_mask;
+ gap = curr_iova->pfn_lo - iovad->start_pfn;
+ if (limit_pfn >= size && new_pfn >= iovad->start_pfn &&
+ gap < candidate_gap) {
+ candidate_gap = gap;
+ candidate_pfn = new_pfn;
+ candidate_rb_parent = curr;
+ }
+
+insert:
+ if (candidate_pfn == ~0UL) {
+ spin_unlock_irqrestore(&iovad->iova_rbtree_lock, flags);
+ return -ENOMEM;
+ }
+
+ /* pfn_lo will point to size aligned address if size_aligned is set */
+ new->pfn_lo = candidate_pfn;
+ new->pfn_hi = new->pfn_lo + size - 1;
+
+ /* If we have 'prev', it's a valid place to start the insertion. */
+ iova_insert_rbtree(&iovad->rbroot, new, candidate_rb_parent);
+ spin_unlock_irqrestore(&iovad->iova_rbtree_lock, flags);
+ return 0;
+}
+
static struct kmem_cache *iova_cache;
static unsigned int iova_cache_users;
static DEFINE_MUTEX(iova_cache_mutex);
@@ -302,8 +366,13 @@ struct iova *
if (!new_iova)
return NULL;

- ret = __alloc_and_insert_iova_range(iovad, size, limit_pfn + 1,
- new_iova, size_aligned);
+ if (iovad->best_fit) {
+ ret = __alloc_and_insert_iova_best_fit(iovad, size,
+ limit_pfn + 1, new_iova, size_aligned);
+ } else {
+ ret = __alloc_and_insert_iova_range(iovad, size, limit_pfn + 1,
+ new_iova, size_aligned);
+ }

if (ret) {
free_iova_mem(new_iova);
diff --git a/include/linux/dma-iommu.h b/include/linux/dma-iommu.h
index 2112f21..b01a31a 100644
--- a/include/linux/dma-iommu.h
+++ b/include/linux/dma-iommu.h
@@ -37,6 +37,8 @@ void iommu_dma_compose_msi_msg(struct msi_desc *desc,

void iommu_dma_get_resv_regions(struct device *dev, struct list_head *list);

+int iommu_dma_enable_best_fit_algo(struct device *dev);
+
#else /* CONFIG_IOMMU_DMA */

struct iommu_domain;
@@ -78,5 +80,10 @@ static inline void iommu_dma_get_resv_regions(struct device *dev, struct list_he
{
}

+static inline int iommu_dma_enable_best_fit_algo(struct device *dev)
+{
+ return -ENODEV;
+}
+
#endif /* CONFIG_IOMMU_DMA */
#endif /* __DMA_IOMMU_H */
diff --git a/include/linux/iova.h b/include/linux/iova.h
index a0637ab..58713bb 100644
--- a/include/linux/iova.h
+++ b/include/linux/iova.h
@@ -95,6 +95,7 @@ struct iova_domain {
flush-queues */
atomic_t fq_timer_on; /* 1 when timer is active, 0
when not */
+ bool best_fit;
};

static inline unsigned long iova_size(struct iova *iova)
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project
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