Re: [PATCH 5/9] mm, drm/ttm, drm/vmwgfx: Support huge TTM pagefaults

[Thomas HellstrÃm (VMware)]

On 1/29/20 3:55 PM, Christian KÃnig wrote:
> Am 24.01.20 um 10:09 schrieb Thomas HellstrÃm (VMware):
> > From: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
> >
> > 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 succeed unless buffer objects and
> > user-space addresses are aligned on huge page size boundaries.
> >
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Michal Hocko <mhocko@xxxxxxxx>
> > Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
> > Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
> > Cc: "JÃrÃme Glisse" <jglisse@xxxxxxxxxx>
> > Cc: "Christian KÃnig" <christian.koenig@xxxxxxx>
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Signed-off-by: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
> > Reviewed-by: Roland Scheidegger <sroland@xxxxxxxxxx>
> > ---
> > Â drivers/gpu/drm/ttm/ttm_bo_vm.cÂÂÂÂÂÂÂÂÂÂÂ | 145 ++++++++++++++++++++-
> > Â drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c |ÂÂ 2 +-
> > Â include/drm/ttm/ttm_bo_api.hÂÂÂÂÂÂÂÂÂÂÂÂÂÂ |ÂÂ 3 +-
> > Â 3 files changed, 145 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c 
> > b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > index 389128b8c4dd..49704261a00d 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > @@ -156,6 +156,89 @@ vm_fault_t ttm_bo_vm_reserve(struct 
> > ttm_buffer_object *bo,
> > Â }
> > Â EXPORT_SYMBOL(ttm_bo_vm_reserve);
> > Â +#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,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ struct ttm_buffer_object *bo,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ pgoff_t page_offset,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ pgoff_t fault_page_size,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ pgprot_t pgprot)
> > +{
> > +ÂÂÂ pgoff_t i;
> > +ÂÂÂ vm_fault_t ret;
> > +ÂÂÂ unsigned long pfn;
> > +ÂÂÂ pfn_t pfnt;
> > +ÂÂÂ struct ttm_tt *ttm = bo->ttm;
> > +ÂÂÂ bool write = vmf->flags & FAULT_FLAG_WRITE;
> > +
> > +ÂÂÂ /* Fault should not cross bo boundary. */
> > +ÂÂÂ page_offset &= ~(fault_page_size - 1);
> > +ÂÂÂ if (page_offset + fault_page_size > bo->num_pages)
> > +ÂÂÂÂÂÂÂ goto out_fallback;
> > +
> > +ÂÂÂ if (bo->mem.bus.is_iomem)
> > +ÂÂÂÂÂÂÂ pfn = ttm_bo_io_mem_pfn(bo, page_offset);
> > +ÂÂÂ else
> > +ÂÂÂÂÂÂÂ pfn = page_to_pfn(ttm->pages[page_offset]);
> > +
> > +ÂÂÂ /* pfn must be fault_page_size aligned. */
> > +ÂÂÂ if ((pfn & (fault_page_size - 1)) != 0)
> > +ÂÂÂÂÂÂÂ goto out_fallback;
> > +
> > +ÂÂÂ /* Check that memory is contiguous. */
> > +ÂÂÂ if (!bo->mem.bus.is_iomem)
> > +ÂÂÂÂÂÂÂ for (i = 1; i < fault_page_size; ++i) {
> > +ÂÂÂÂÂÂÂÂÂÂÂ if (page_to_pfn(ttm->pages[page_offset + i]) != pfn + i)
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ goto out_fallback;
> > +ÂÂÂÂÂÂÂ }
> > +ÂÂÂ /* IO mem without the io_mem_pfn callback is always contiguous. */
> > +ÂÂÂ else if (bo->bdev->driver->io_mem_pfn)
> > +ÂÂÂÂÂÂÂ for (i = 1; i < fault_page_size; ++i) {
> > +ÂÂÂÂÂÂÂÂÂÂÂ if (ttm_bo_io_mem_pfn(bo, page_offset + i) != pfn + i)
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ goto out_fallback;
> > +ÂÂÂÂÂÂÂ }
>
> Maybe add {} to the if to make clear where things start/end.
>
> > +
> > +ÂÂÂ pfnt = __pfn_to_pfn_t(pfn, PFN_DEV);
> > +ÂÂÂ if (fault_page_size == (HPAGE_PMD_SIZE >> PAGE_SHIFT))
> > +ÂÂÂÂÂÂÂ ret = vmf_insert_pfn_pmd_prot(vmf, pfnt, pgprot, write);
> > +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> > +ÂÂÂ else if (fault_page_size == (HPAGE_PUD_SIZE >> PAGE_SHIFT))
> > +ÂÂÂÂÂÂÂ ret = vmf_insert_pfn_pud_prot(vmf, pfnt, pgprot, write);
> > +#endif
> > +ÂÂÂ else
> > +ÂÂÂÂÂÂÂ WARN_ON_ONCE(ret = VM_FAULT_FALLBACK);
> > +
> > +ÂÂÂ if (ret != VM_FAULT_NOPAGE)
> > +ÂÂÂÂÂÂÂ goto out_fallback;
> > +
> > +ÂÂÂ return VM_FAULT_NOPAGE;
> > +out_fallback:
> > +ÂÂÂ count_vm_event(THP_FAULT_FALLBACK);
> > +ÂÂÂ return VM_FAULT_FALLBACK;
>
> This doesn't seem to match the function documentation since we never 
> return ret here as far as I can see.
>
> Apart from those comments it looks like that should work,
> Christian.


Thanks for reviewing, Christian. I'll update the next version with your 
feedback.

/Thomas