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Message-ID: <b7e21292-2967-b11c-a0b6-8b857c89f9df@amd.com>
Date: Wed, 27 Nov 2019 10:12:41 +0100
From: Christian König <christian.koenig@....com>
To: Thomas Hellström (VMware)
<thomas_os@...pmail.org>, dri-devel@...ts.freedesktop.org,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
linux-graphics-maintainer@...are.com
Cc: Thomas Hellstrom <thellstrom@...are.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Michal Hocko <mhocko@...e.com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Ralph Campbell <rcampbell@...dia.com>,
Jérôme Glisse <jglisse@...hat.com>
Subject: Re: [RFC PATCH 4/7] drm/ttm: Support huge pagefaults
Am 27.11.19 um 09:31 schrieb Thomas Hellström (VMware):
> From: Thomas Hellstrom <thellstrom@...are.com>
>
> Support huge (PMD-size and PUD-size) page-table entries by providing a
> huge_fault() callback.
> We still support private mappings and write-notify by splitting the huge
> page-table entries on write-access.
>
> Note that for huge page-faults to occur, either the kernel needs to be
> compiled with trans-huge-pages always enabled, or the kernel needs to be
> compiled with trans-huge-pages enabled using madvise, and the user-space
> app needs to call madvise() to enable trans-huge pages on a per-mapping
> basis.
>
> Furthermore huge page-faults will not occur unless buffer objects and
> user-space addresses are aligned on huge page size boundaries.
>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Cc: Ralph Campbell <rcampbell@...dia.com>
> Cc: "Jérôme Glisse" <jglisse@...hat.com>
> Cc: "Christian König" <christian.koenig@....com>
> Signed-off-by: Thomas Hellstrom <thellstrom@...are.com>
> ---
> drivers/gpu/drm/ttm/ttm_bo_vm.c | 139 +++++++++++++++++++++++++++++++-
> include/drm/ttm/ttm_bo_api.h | 3 +-
> 2 files changed, 138 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index 2098f8d4dfc5..8d6089880e39 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -150,6 +150,84 @@ vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
> }
> EXPORT_SYMBOL(ttm_bo_vm_reserve);
>
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +/**
> + * ttm_bo_vm_insert_huge - Insert a pfn for PUD or PMD faults
> + * @vmf: Fault data
> + * @bo: The buffer object
> + * @page_offset: Page offset from bo start
> + * @fault_page_size: The size of the fault in pages.
> + * @pgprot: The page protections.
> + * Does additional checking whether it's possible to insert a PUD or PMD
> + * pfn and performs the insertion.
> + *
> + * Return: VM_FAULT_NOPAGE on successful insertion, VM_FAULT_FALLBACK if
> + * a huge fault was not possible, and a VM_FAULT_ERROR code otherwise.
> + */
> +static vm_fault_t ttm_bo_vm_insert_huge(struct vm_fault *vmf,
> + struct ttm_buffer_object *bo,
> + pgoff_t page_offset,
> + pgoff_t fault_page_size,
> + pgprot_t pgprot)
> +{
> + pgoff_t i;
> + vm_fault_t ret;
> + unsigned long pfn;
> + pfn_t pfnt;
> + struct ttm_tt *ttm = bo->ttm;
> + bool write = vmf->flags & FAULT_FLAG_WRITE;
> +
> +
> + /* Fault should not cross bo boundary */
> + page_offset &= ~(fault_page_size - 1);
> + if (page_offset + fault_page_size > bo->num_pages)
> + goto out_fallback;
> +
> + if (bo->mem.bus.is_iomem)
> + pfn = ttm_bo_io_mem_pfn(bo, page_offset);
> + else
> + pfn = page_to_pfn(ttm->pages[page_offset]);
> +
> + /* pfn must be fault_page_size aligned. */
> + if ((pfn & (fault_page_size - 1)) != 0)
> + goto out_fallback;
> +
> + /* IO memory is OK now, TT memory must be contigous. */
That won't work correctly, IO mem might not be contiguous either.
We either need to call ttm_bo_io_mem_pfn() multiple times and check that
the addresses are linear or return the length additional to the pfn.
Regards,
Christian.
> + if (!bo->mem.bus.is_iomem)
> + for (i = 1; i < fault_page_size; ++i) {
> + if (page_to_pfn(ttm->pages[page_offset + i]) != pfn + i)
> + goto out_fallback;
> + }
> +
> + pfnt = __pfn_to_pfn_t(pfn, PFN_DEV);
> + if (fault_page_size == (HPAGE_PMD_SIZE >> PAGE_SHIFT))
> + ret = vmf_insert_pfn_pmd_prot(vmf, pfnt, pgprot, write);
> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> + else if (fault_page_size == (HPAGE_PUD_SIZE >> PAGE_SHIFT))
> + ret = vmf_insert_pfn_pud_prot(vmf, pfnt, pgprot, write);
> +#endif
> + else
> + WARN_ON_ONCE(ret = VM_FAULT_FALLBACK);
> +
> + if (ret != VM_FAULT_NOPAGE)
> + goto out_fallback;
> +
> + return VM_FAULT_NOPAGE;
> +out_fallback:
> + count_vm_event(THP_FAULT_FALLBACK);
> + return VM_FAULT_FALLBACK;
> +}
> +#else
> +static vm_fault_t ttm_bo_vm_insert_huge(struct vm_fault *vmf,
> + struct ttm_buffer_object *bo,
> + pgoff_t page_offset,
> + pgoff_t fault_page_size,
> + pgprot_t pgprot)
> +{
> + return VM_FAULT_NOPAGE;
> +}
> +#endif
> +
> /**
> * ttm_bo_vm_fault_reserved - TTM fault helper
> * @vmf: The struct vm_fault given as argument to the fault callback
> @@ -170,7 +248,8 @@ EXPORT_SYMBOL(ttm_bo_vm_reserve);
> */
> vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
> pgprot_t prot,
> - pgoff_t num_prefault)
> + pgoff_t num_prefault,
> + pgoff_t fault_page_size)
> {
> struct vm_area_struct *vma = vmf->vma;
> struct ttm_buffer_object *bo = vma->vm_private_data;
> @@ -262,6 +341,13 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
> prot = pgprot_decrypted(prot);
> }
>
> + /* We don't prefault on huge faults. Yet. */
> + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && fault_page_size != 1) {
> + ret = ttm_bo_vm_insert_huge(vmf, bo, page_offset,
> + fault_page_size, prot);
> + goto out_io_unlock;
> + }
> +
> /*
> * Speculatively prefault a number of pages. Only error on
> * first page.
> @@ -320,7 +406,7 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> return ret;
>
> prot = vma->vm_page_prot;
> - ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT);
> + ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, 1);
> if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
> return ret;
>
> @@ -330,6 +416,50 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> }
> EXPORT_SYMBOL(ttm_bo_vm_fault);
>
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static vm_fault_t ttm_bo_vm_huge_fault(struct vm_fault *vmf,
> + enum page_entry_size pe_size)
> +{
> + struct vm_area_struct *vma = vmf->vma;
> + pgprot_t prot;
> + struct ttm_buffer_object *bo = vma->vm_private_data;
> + vm_fault_t ret;
> + pgoff_t fault_page_size = 0;
> + bool write = vmf->flags & FAULT_FLAG_WRITE;
> +
> + switch (pe_size) {
> + case PE_SIZE_PMD:
> + fault_page_size = HPAGE_PMD_SIZE >> PAGE_SHIFT;
> + break;
> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> + case PE_SIZE_PUD:
> + fault_page_size = HPAGE_PUD_SIZE >> PAGE_SHIFT;
> + break;
> +#endif
> + default:
> + WARN_ON_ONCE(1);
> + return VM_FAULT_FALLBACK;
> + }
> +
> + /* Fallback on write dirty-tracking or COW */
> + if (write && !(pgprot_val(vmf->vma->vm_page_prot) & _PAGE_RW))
> + return VM_FAULT_FALLBACK;
> +
> + ret = ttm_bo_vm_reserve(bo, vmf);
> + if (ret)
> + return ret;
> +
> + prot = vm_get_page_prot(vma->vm_flags);
> + ret = ttm_bo_vm_fault_reserved(vmf, prot, 1, fault_page_size);
> + if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
> + return ret;
> +
> + dma_resv_unlock(bo->base.resv);
> +
> + return ret;
> +}
> +#endif
> +
> void ttm_bo_vm_open(struct vm_area_struct *vma)
> {
> struct ttm_buffer_object *bo = vma->vm_private_data;
> @@ -431,7 +561,10 @@ static const struct vm_operations_struct ttm_bo_vm_ops = {
> .fault = ttm_bo_vm_fault,
> .open = ttm_bo_vm_open,
> .close = ttm_bo_vm_close,
> - .access = ttm_bo_vm_access
> + .access = ttm_bo_vm_access,
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> + .huge_fault = ttm_bo_vm_huge_fault,
> +#endif
> };
>
> static struct ttm_buffer_object *ttm_bo_vm_lookup(struct ttm_bo_device *bdev,
> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> index 66ca49db9633..4fc90d53aa15 100644
> --- a/include/drm/ttm/ttm_bo_api.h
> +++ b/include/drm/ttm/ttm_bo_api.h
> @@ -732,7 +732,8 @@ vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
>
> vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
> pgprot_t prot,
> - pgoff_t num_prefault);
> + pgoff_t num_prefault,
> + pgoff_t fault_page_size);
>
> vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf);
>
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