On Thu, May 12, 2022 at 05:33:44PM -0500, Sierra Guiza, Alejandro (Alex) wrote: > > On 5/11/2022 1:50 PM, Jason Gunthorpe wrote: > > On Thu, May 05, 2022 at 04:34:36PM -0500, Alex Sierra wrote: > > > > > diff --git a/mm/memory.c b/mm/memory.c > > > index 76e3af9639d9..892c4cc54dc2 100644 > > > +++ b/mm/memory.c > > > @@ -621,6 +621,13 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, > > > if (is_zero_pfn(pfn)) > > > return NULL; > > > if (pte_devmap(pte)) > > > +/* > > > + * NOTE: Technically this should goto check_pfn label. However, page->_mapcount > > > + * is never incremented for device pages that are mmap through DAX mechanism > > > + * using pmem driver mounted into ext4 filesystem. When these pages are unmap, > > > + * zap_pte_range is called and vm_normal_page return a valid page with > > > + * page_mapcount() = 0, before page_remove_rmap is called. > > > + */ > > > return NULL; > > ? Where does this series cause device coherent to be returned? > In our case, device coherent pages could be obtained as a result of > migration(Patches 6/7 of 15), ending up mapped in CPU page tables. Later on, > these pages might need to be returned by get_user_pages or other callers > through vm_normal_pages. Our approach in this series, is to handle > device-coherent-managed pages returned by vm_normal_pages, inside each > caller. EX. device coherent pages don’t support LRU lists, NUMA migration or > THP. > > > > Wasn't the plan to not set pte_devmap() ? > > amdgpu does not set pte_devmap for our DEVICE_COHERENT pages. DEVMAP flags > are set by drivers like virtio_fs or pmem, where MEMORY_DEVICE_FS_DAX type > is used. > This patch series deals with DEVICE_COHERENT pages. My understanding was, > that the DAX code and DEVICE_GENERIC would be fixed up later by someone more > familiar with it. Were you expecting that we'd fix the DAX usage of > pte_devmap flags in this patch series as well? No, I was just trying to find where the pages got inserted and understand the comment above. I think the comment should be clarified more like you explained: New uers of ZONE_DEVICE will not set pte_devmap() and will have refcounts incremented on their struct pages when they are inserted into PTEs, thus they are safe to return here. Legacy ZONE_DEVICE pages that set pte_devmap() do not have refcounts. .... Jason
