Messages in this thread | | | Date | Wed, 8 May 2024 09:15:29 +0200 | Subject | Re: [PATCH 2/8] mm: memory: extend finish_fault() to support large folio | From | David Hildenbrand <> |
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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.
We should try doing this as cleanly as possible, to prepare for the future / corner cases.
-- Cheers,
David / dhildenb
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