| Message ID | 20200220122719.4302-1-thomas_os@shipmail.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | Huge page-table entries for TTM | expand |
Andrew, Michal I'm wondering what's the best way here to get the patches touching mm reviewed and accepted? While drm people and VMware internal people have looked at them, I think the huge_fault() fallback splitting and the introduction of vma_is_special_huge() needs looking at more thoroughly. Apart from that, if possible, I think the best way to merge this series is also through a DRM tree. Thanks, Thomas On 2/20/20 1:27 PM, Thomas Hellström (VMware) wrote: > In order to reduce TLB misses and CPU usage this patchset enables huge- > and giant page-table entries for TTM and TTM-enabled graphics drivers. > > Patch 1 and 2 introduce a vma_is_special_huge() function to make the mm code > take the same path as DAX when splitting huge- and giant page table entries, > (which currently means zapping the page-table entry and rely on re-faulting). > > Patch 3 makes the mm code split existing huge page-table entries > on huge_fault fallbacks. Typically on COW or on buffer-objects that want > write-notify. COW and write-notification is always done on the lowest > page-table level. See the patch log message for additional considerations. > > Patch 4 introduces functions to allow the graphics drivers to manipulate > the caching- and encryption flags of huge page-table entries without ugly > hacks. > > Patch 5 implements the huge_fault handler in TTM. > This enables huge page-table entries, provided that the kernel is configured > to support transhuge pages, either by default or using madvise(). > However, they are unlikely to be inserted unless the kernel buffer object > pfns and user-space addresses align perfectly. There are various options > here, but since buffer objects that reside in system pages typically start > at huge page boundaries if they are backed by huge pages, we try to enforce > buffer object starting pfns and user-space addresses to be huge page-size > aligned if their size exceeds a huge page-size. If pud-size transhuge > ("giant") pages are enabled by the arch, the same holds for those. > > Patch 6 implements a specialized huge_fault handler for vmwgfx. > The vmwgfx driver may perform dirty-tracking and needs some special code > to handle that correctly. > > Patch 7 implements a drm helper to align user-space addresses according > to the above scheme, if possible. > > Patch 8 implements a TTM range manager for vmwgfx that does the same for > graphics IO memory. This may later be reused by other graphics drivers > if necessary. > > Patch 9 finally hooks up the helpers of patch 7 and 8 to the vmwgfx driver. > A similar change is needed for graphics drivers that want a reasonable > likelyhood of actually using huge page-table entries. > > If a buffer object size is not huge-page or giant-page aligned, > its size will NOT be inflated by this patchset. This means that the buffer > object tail will use smaller size page-table entries and thus no memory > overhead occurs. Drivers that want to pay the memory overhead price need to > implement their own scheme to inflate buffer-object sizes. > > PMD size huge page-table-entries have been tested with vmwgfx and found to > work well both with system memory backed and IO memory backed buffer objects. > > PUD size giant page-table-entries have seen limited (fault and COW) testing > using a modified kernel (to support 1GB page allocations) and a fake vmwgfx > TTM memory type. The vmwgfx driver does otherwise not support 1GB-size IO > memory resources. > > Comments and suggestions welcome. > Thomas > > Changes since RFC: > * Check for buffer objects present in contigous IO Memory (Christian König) > * Rebased on the vmwgfx emulated coherent memory functionality. That rebase > adds patch 5. > Changes since v1: > * Make the new TTM range manager vmwgfx-specific. (Christian König) > * Minor fixes for configs that don't support or only partially support > transhuge pages. > Changes since v2: > * Minor coding style and doc fixes in patch 5/9 (Christian König) > * Patch 5/9 doesn't touch mm. Remove from the patch title. > Changes since v3: > * Added reviews and acks > * Implemented ugly but generic ttm_pgprot_is_wrprotecting() instead of arch > specific code. > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Michal Hocko <mhocko@suse.com> > Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> > Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> > Cc: Ralph Campbell <rcampbell@nvidia.com> > Cc: "Jérôme Glisse" <jglisse@redhat.com> > Cc: "Christian König" <christian.koenig@amd.com> > Cc: Dan Williams <dan.j.williams@intel.com> > > > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel
On Fri, 28 Feb 2020 14:08:04 +0100 Thomas Hellström (VMware) <thomas_os@shipmail.org> wrote: > I'm wondering what's the best way here to get the patches touching mm > reviewed and accepted? > While drm people and VMware internal people have looked at them, I think > the huge_fault() fallback splitting and the introduction of > vma_is_special_huge() needs looking at more thoroughly. > > Apart from that, if possible, I think the best way to merge this series > is also through a DRM tree. Patches 1-3 look OK to me. I just had a few commenting/changelogging niggles.
On Thu, 20 Feb 2020 13:27:15 +0100 Thomas Hellstrom wrote: > + > +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 && ttm_pgprot_is_wrprotecting(vma->vm_page_prot)) > + 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; Seems it does not make much sense to check VM_FAULT_RETRY and return as at least resv lock is left behind without care. > + > + dma_resv_unlock(bo->base.resv); > + > + return ret; > +}
On Sun, 2020-03-01 at 21:49 +0800, Hillf Danton wrote: > On Thu, 20 Feb 2020 13:27:15 +0100 Thomas Hellstrom wrote: > > + > > +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 && ttm_pgprot_is_wrprotecting(vma->vm_page_prot)) > > + 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; > > Seems it does not make much sense to check VM_FAULT_RETRY and return > as > at least resv lock is left behind without care. With this particular flag combination, both the mm_sem and the dma_resv lock have already been released by TTM. It's a special case allowing for drivers to release the mmap_sem when waiting for IO. That should probably be documented better in TTM. /Thomas
On Fri 28-02-20 14:08:04, Thomas Hellström (VMware) wrote: > Andrew, Michal > > I'm wondering what's the best way here to get the patches touching mm > reviewed and accepted? I am sorry, but I am busy with other stuff and unlikely to find time to review this series.
On 3/1/20 5:04 AM, Andrew Morton wrote: > On Fri, 28 Feb 2020 14:08:04 +0100 Thomas Hellström (VMware) <thomas_os@shipmail.org> wrote: > >> I'm wondering what's the best way here to get the patches touching mm >> reviewed and accepted? >> While drm people and VMware internal people have looked at them, I think >> the huge_fault() fallback splitting and the introduction of >> vma_is_special_huge() needs looking at more thoroughly. >> >> Apart from that, if possible, I think the best way to merge this series >> is also through a DRM tree. > Patches 1-3 look OK to me. I just had a few commenting/changelogging > niggles. Thanks for reviewing, Andrew. I just updated the series following your comments. Thanks, Thomas
In order to reduce TLB misses and CPU usage this patchset enables huge- and giant page-table entries for TTM and TTM-enabled graphics drivers. Patch 1 and 2 introduce a vma_is_special_huge() function to make the mm code take the same path as DAX when splitting huge- and giant page table entries, (which currently means zapping the page-table entry and rely on re-faulting). Patch 3 makes the mm code split existing huge page-table entries on huge_fault fallbacks. Typically on COW or on buffer-objects that want write-notify. COW and write-notification is always done on the lowest page-table level. See the patch log message for additional considerations. Patch 4 introduces functions to allow the graphics drivers to manipulate the caching- and encryption flags of huge page-table entries without ugly hacks. Patch 5 implements the huge_fault handler in TTM. This enables huge page-table entries, provided that the kernel is configured to support transhuge pages, either by default or using madvise(). However, they are unlikely to be inserted unless the kernel buffer object pfns and user-space addresses align perfectly. There are various options here, but since buffer objects that reside in system pages typically start at huge page boundaries if they are backed by huge pages, we try to enforce buffer object starting pfns and user-space addresses to be huge page-size aligned if their size exceeds a huge page-size. If pud-size transhuge ("giant") pages are enabled by the arch, the same holds for those. Patch 6 implements a specialized huge_fault handler for vmwgfx. The vmwgfx driver may perform dirty-tracking and needs some special code to handle that correctly. Patch 7 implements a drm helper to align user-space addresses according to the above scheme, if possible. Patch 8 implements a TTM range manager for vmwgfx that does the same for graphics IO memory. This may later be reused by other graphics drivers if necessary. Patch 9 finally hooks up the helpers of patch 7 and 8 to the vmwgfx driver. A similar change is needed for graphics drivers that want a reasonable likelyhood of actually using huge page-table entries. If a buffer object size is not huge-page or giant-page aligned, its size will NOT be inflated by this patchset. This means that the buffer object tail will use smaller size page-table entries and thus no memory overhead occurs. Drivers that want to pay the memory overhead price need to implement their own scheme to inflate buffer-object sizes. PMD size huge page-table-entries have been tested with vmwgfx and found to work well both with system memory backed and IO memory backed buffer objects. PUD size giant page-table-entries have seen limited (fault and COW) testing using a modified kernel (to support 1GB page allocations) and a fake vmwgfx TTM memory type. The vmwgfx driver does otherwise not support 1GB-size IO memory resources. Comments and suggestions welcome. Thomas Changes since RFC: * Check for buffer objects present in contigous IO Memory (Christian König) * Rebased on the vmwgfx emulated coherent memory functionality. That rebase adds patch 5. Changes since v1: * Make the new TTM range manager vmwgfx-specific. (Christian König) * Minor fixes for configs that don't support or only partially support transhuge pages. Changes since v2: * Minor coding style and doc fixes in patch 5/9 (Christian König) * Patch 5/9 doesn't touch mm. Remove from the patch title. Changes since v3: * Added reviews and acks * Implemented ugly but generic ttm_pgprot_is_wrprotecting() instead of arch specific code. Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Michal Hocko <mhocko@suse.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Ralph Campbell <rcampbell@nvidia.com> Cc: "Jérôme Glisse" <jglisse@redhat.com> Cc: "Christian König" <christian.koenig@amd.com> Cc: Dan Williams <dan.j.williams@intel.com>