Messages in this thread | | | Date | Wed, 8 May 2024 17:06:28 +0800 | Subject | Re: [PATCH 2/8] mm: memory: extend finish_fault() to support large folio | From | Baolin Wang <> |
| |
On 2024/5/8 15:15, David Hildenbrand wrote: > On 08.05.24 05:44, Baolin Wang wrote: >> >> >> On 2024/5/7 18:37, Ryan Roberts wrote: >>> On 06/05/2024 09:46, Baolin Wang wrote: >>>> Add large folio mapping establishment support for finish_fault() as >>>> a preparation, >>>> to support multi-size THP allocation of anonymous shmem pages in the >>>> following >>>> patches. >>>> >>>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> >>>> --- >>>> mm/memory.c | 43 +++++++++++++++++++++++++++++++++---------- >>>> 1 file changed, 33 insertions(+), 10 deletions(-) >>>> >>>> diff --git a/mm/memory.c b/mm/memory.c >>>> index eea6e4984eae..936377220b77 100644 >>>> --- a/mm/memory.c >>>> +++ b/mm/memory.c >>>> @@ -4747,9 +4747,12 @@ vm_fault_t finish_fault(struct vm_fault *vmf) >>>> { >>>> struct vm_area_struct *vma = vmf->vma; >>>> struct page *page; >>>> + struct folio *folio; >>>> vm_fault_t ret; >>>> bool is_cow = (vmf->flags & FAULT_FLAG_WRITE) && >>>> !(vma->vm_flags & VM_SHARED); >>>> + int type, nr_pages, i; >>>> + unsigned long addr = vmf->address; >>>> /* Did we COW the page? */ >>>> if (is_cow) >>>> @@ -4780,24 +4783,44 @@ vm_fault_t finish_fault(struct vm_fault *vmf) >>>> return VM_FAULT_OOM; >>>> } >>>> + folio = page_folio(page); >>>> + nr_pages = folio_nr_pages(folio); >>>> + >>>> + if (unlikely(userfaultfd_armed(vma))) { >>>> + nr_pages = 1; >>>> + } else if (nr_pages > 1) { >>>> + unsigned long start = ALIGN_DOWN(vmf->address, nr_pages * >>>> PAGE_SIZE); >>>> + unsigned long end = start + nr_pages * PAGE_SIZE; >>>> + >>>> + /* In case the folio size in page cache beyond the VMA >>>> limits. */ >>>> + addr = max(start, vma->vm_start); >>>> + nr_pages = (min(end, vma->vm_end) - addr) >> PAGE_SHIFT; >>>> + >>>> + page = folio_page(folio, (addr - start) >> PAGE_SHIFT); >>> >>> I still don't really follow the logic in this else if block. Isn't it >>> possible >>> that finish_fault() gets called with a page from a folio that isn't >>> aligned with >>> vmf->address? >>> >>> For example, let's say we have a file who's size is 64K and which is >>> cached in a >>> single large folio in the page cache. But the file is mapped into a >>> process at >>> VA 16K to 80K. Let's say we fault on the first page (VA=16K). You >>> will calculate >> >> For shmem, this doesn't happen because the VA is aligned with the >> hugepage size in the shmem_get_unmapped_area() function. See patch 7. > > Does that cover mremap() and MAP_FIXED as well.
Good point. Thanks for pointing this out.
> We should try doing this as cleanly as possible, to prepare for the > future / corner cases.
Sure. Let me re-think about the algorithm.
| |