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Message-ID: <20250711153523.42d68ec0.alex.williamson@redhat.com>
Date: Fri, 11 Jul 2025 15:35:23 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: lizhe.67@...edance.com
Cc: akpm@...ux-foundation.org, david@...hat.com, jgg@...pe.ca,
peterx@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH v4 2/5] vfio/type1: optimize vfio_pin_pages_remote()
On Thu, 10 Jul 2025 16:53:52 +0800
lizhe.67@...edance.com wrote:
> 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.
> Batch processing of statistical counting operations can effectively enhance
> performance.
>
> In addition, the pages obtained through longterm GUP are neither invalid
> nor reserved. Therefore, we can reduce the overhead associated with some
> calls to function is_invalid_reserved_pfn().
>
> The performance test results for completing the 16G VFIO IOMMU DMA mapping
> are as follows.
>
> Base(v6.16-rc4):
> ------- AVERAGE (MADV_HUGEPAGE) --------
> VFIO MAP DMA in 0.047 s (340.2 GB/s)
> ------- AVERAGE (MAP_POPULATE) --------
> VFIO MAP DMA in 0.280 s (57.2 GB/s)
> ------- AVERAGE (HUGETLBFS) --------
> VFIO MAP DMA in 0.052 s (310.5 GB/s)
>
> With this patch:
> ------- AVERAGE (MADV_HUGEPAGE) --------
> VFIO MAP DMA in 0.027 s (602.1 GB/s)
> ------- AVERAGE (MAP_POPULATE) --------
> VFIO MAP DMA in 0.257 s (62.4 GB/s)
> ------- AVERAGE (HUGETLBFS) --------
> VFIO MAP DMA in 0.031 s (517.4 GB/s)
>
> For large folio, we achieve an over 40% performance improvement.
> For small folios, the performance test results indicate a
> slight improvement.
>
> 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>
> Acked-by: David Hildenbrand <david@...hat.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 83 ++++++++++++++++++++++++++++-----
> 1 file changed, 71 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 1136d7ac6b59..6909275e46c2 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -318,7 +318,13 @@ 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 highest vfio_pfn that overlapping the range
> + * [iova_start, iova_end) in rb tree.
> + */
> +static struct vfio_pfn *vfio_find_vpfn_range(struct vfio_dma *dma,
> + dma_addr_t iova_start, dma_addr_t iova_end)
> {
> struct vfio_pfn *vpfn;
> struct rb_node *node = dma->pfn_list.rb_node;
> @@ -326,9 +332,9 @@ static struct vfio_pfn *vfio_find_vpfn(struct vfio_dma *dma, dma_addr_t iova)
> while (node) {
> vpfn = rb_entry(node, struct vfio_pfn, node);
>
> - if (iova < vpfn->iova)
> + if (iova_end <= vpfn->iova)
> node = node->rb_left;
> - else if (iova > vpfn->iova)
> + else if (iova_start > vpfn->iova)
> node = node->rb_right;
> else
> return vpfn;
> @@ -336,6 +342,11 @@ 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, iova + PAGE_SIZE);
> +}
> +
> static void vfio_link_pfn(struct vfio_dma *dma,
> struct vfio_pfn *new)
> {
> @@ -614,6 +625,39 @@ static long vaddr_get_pfns(struct mm_struct *mm, unsigned long vaddr,
> return ret;
> }
>
> +
> +static long vpfn_pages(struct vfio_dma *dma,
> + dma_addr_t iova_start, long nr_pages)
> +{
> + dma_addr_t iova_end = iova_start + (nr_pages << PAGE_SHIFT);
> + struct vfio_pfn *top = vfio_find_vpfn_range(dma, iova_start, iova_end);
> + long ret = 1;
> + struct vfio_pfn *vpfn;
> + struct rb_node *prev;
> + struct rb_node *next;
> +
> + if (likely(!top))
> + return 0;
> +
> + prev = next = &top->node;
> +
> + while ((prev = rb_prev(prev))) {
> + vpfn = rb_entry(prev, struct vfio_pfn, node);
> + if (vpfn->iova < iova_start)
> + break;
> + ret++;
> + }
> +
> + while ((next = rb_next(next))) {
> + vpfn = rb_entry(next, struct vfio_pfn, node);
> + if (vpfn->iova >= iova_end)
> + break;
> + ret++;
> + }
> +
> + return ret;
> +}
> +
> /*
> * Attempt to pin pages. We really don't want to track all the pfns and
> * the iommu can only map chunks of consecutive pfns anyway, so get the
> @@ -680,32 +724,47 @@ 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) {
> + long nr_pages, acct_pages = 0;
> +
> if (pfn != *pfn_base + pinned ||
> rsvd != is_invalid_reserved_pfn(pfn))
> goto out;
>
> + /*
> + * Using GUP with the FOLL_LONGTERM in
> + * vaddr_get_pfns() will not return invalid
> + * or reserved pages.
> + */
> + nr_pages = num_pages_contiguous(
> + &batch->pages[batch->offset],
> + batch->size);
> + if (!rsvd) {
> + acct_pages = nr_pages;
> + acct_pages -= vpfn_pages(dma, iova, nr_pages);
> + }
> +
> /*
> * 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 (acct_pages) {
> if (!dma->lock_cap &&
> - mm->locked_vm + lock_acct + 1 > limit) {
> + mm->locked_vm + lock_acct + acct_pages > limit) {
Don't resend, I'll fix on commit, but there's still a gratuitous
difference in leading white space from the original. Otherwise the
series looks good to me but I'll give Jason a little more time to
provide reviews since he's been so active in the thread (though he'd
rather we just use iommufd ;). Thanks,
Alex
> pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n",
> __func__, limit << PAGE_SHIFT);
> ret = -ENOMEM;
> goto unpin_out;
> }
> - lock_acct++;
> + lock_acct += acct_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;
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