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Message-ID: <20250521042507.77205-1-lizhe.67@bytedance.com>
Date: Wed, 21 May 2025 12:25:07 +0800
From: lizhe.67@...edance.com
To: alex.williamson@...hat.com
Cc: david@...hat.com,
kvm@...r.kernel.org,
linux-kernel@...r.kernel.org,
muchun.song@...ux.dev,
peterx@...hat.com,
lizhe.67@...edance.com
Subject: [PATCH v4] vfio/type1: optimize vfio_pin_pages_remote() for large folios
From: Li Zhe <lizhe.67@...edance.com>
When vfio_pin_pages_remote() is called with a range of addresses that
includes large folios, the function currently performs individual
statistics counting operations for each page. This can lead to significant
performance overheads, especially when dealing with large ranges of pages.
This patch optimize this process by batching the statistics counting
operations.
The performance test results for completing the 8G VFIO IOMMU DMA mapping,
obtained through trace-cmd, are as follows. In this case, the 8G virtual
address space has been mapped to physical memory using hugetlbfs with
pagesize=2M.
Before this patch:
funcgraph_entry: # 33813.703 us | vfio_pin_map_dma();
After this patch:
funcgraph_entry: # 16071.378 us | vfio_pin_map_dma();
Signed-off-by: Li Zhe <lizhe.67@...edance.com>
Co-developed-by: Alex Williamson <alex.williamson@...hat.com>
Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
---
Changelogs:
v3->v4:
- Use min_t() to obtain the step size, rather than min().
- Fix some issues in commit message and title.
v2->v3:
- Code simplification.
- Fix some issues in comments.
v1->v2:
- Fix some issues in comments and formatting.
- Consolidate vfio_find_vpfn_range() and vfio_find_vpfn().
- Move the processing logic for hugetlbfs folio into the while(true) loop
and use a variable with a default value of 1 to indicate the number of
consecutive pages.
v3 patch: https://lore.kernel.org/all/20250520070020.6181-1-lizhe.67@bytedance.com/
v2 patch: https://lore.kernel.org/all/20250519070419.25827-1-lizhe.67@bytedance.com/
v1 patch: https://lore.kernel.org/all/20250513035730.96387-1-lizhe.67@bytedance.com/
drivers/vfio/vfio_iommu_type1.c | 48 +++++++++++++++++++++++++--------
1 file changed, 37 insertions(+), 11 deletions(-)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 0ac56072af9f..bd46ed9361fe 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -319,15 +319,22 @@ static void vfio_dma_bitmap_free_all(struct vfio_iommu *iommu)
/*
* Helper Functions for host iova-pfn list
*/
-static struct vfio_pfn *vfio_find_vpfn(struct vfio_dma *dma, dma_addr_t iova)
+
+/*
+ * Find the first vfio_pfn that overlapping the range
+ * [iova, iova + PAGE_SIZE * npage) in rb tree.
+ */
+static struct vfio_pfn *vfio_find_vpfn_range(struct vfio_dma *dma,
+ dma_addr_t iova, unsigned long npage)
{
struct vfio_pfn *vpfn;
struct rb_node *node = dma->pfn_list.rb_node;
+ dma_addr_t end_iova = iova + PAGE_SIZE * npage;
while (node) {
vpfn = rb_entry(node, struct vfio_pfn, node);
- if (iova < vpfn->iova)
+ if (end_iova <= vpfn->iova)
node = node->rb_left;
else if (iova > vpfn->iova)
node = node->rb_right;
@@ -337,6 +344,11 @@ static struct vfio_pfn *vfio_find_vpfn(struct vfio_dma *dma, dma_addr_t iova)
return NULL;
}
+static inline struct vfio_pfn *vfio_find_vpfn(struct vfio_dma *dma, dma_addr_t iova)
+{
+ return vfio_find_vpfn_range(dma, iova, 1);
+}
+
static void vfio_link_pfn(struct vfio_dma *dma,
struct vfio_pfn *new)
{
@@ -681,32 +693,46 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
* and rsvd here, and therefore continues to use the batch.
*/
while (true) {
+ struct folio *folio = page_folio(batch->pages[batch->offset]);
+ long nr_pages;
+
if (pfn != *pfn_base + pinned ||
rsvd != is_invalid_reserved_pfn(pfn))
goto out;
+ /*
+ * Note: The current nr_pages does not achieve the optimal
+ * performance in scenarios where folio_nr_pages() exceeds
+ * batch->capacity. It is anticipated that future enhancements
+ * will address this limitation.
+ */
+ nr_pages = min_t(long, batch->size, folio_nr_pages(folio) -
+ folio_page_idx(folio, batch->pages[batch->offset]));
+ if (nr_pages > 1 && vfio_find_vpfn_range(dma, iova, nr_pages))
+ nr_pages = 1;
+
/*
* Reserved pages aren't counted against the user,
* externally pinned pages are already counted against
* the user.
*/
- if (!rsvd && !vfio_find_vpfn(dma, iova)) {
+ if (!rsvd && (nr_pages > 1 || !vfio_find_vpfn(dma, iova))) {
if (!dma->lock_cap &&
- mm->locked_vm + lock_acct + 1 > limit) {
+ mm->locked_vm + lock_acct + nr_pages > limit) {
pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n",
__func__, limit << PAGE_SHIFT);
ret = -ENOMEM;
goto unpin_out;
}
- lock_acct++;
+ lock_acct += nr_pages;
}
- pinned++;
- npage--;
- vaddr += PAGE_SIZE;
- iova += PAGE_SIZE;
- batch->offset++;
- batch->size--;
+ pinned += nr_pages;
+ npage -= nr_pages;
+ vaddr += PAGE_SIZE * nr_pages;
+ iova += PAGE_SIZE * nr_pages;
+ batch->offset += nr_pages;
+ batch->size -= nr_pages;
if (!batch->size)
break;
--
2.20.1
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