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@xxxxxxxxxxxxxxxxx>
---
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
