Re: [PATCH 3/9] userfaultfd/shmem: support minor fault registration for shmem

On Thu, Apr 08, 2021 at 04:43:21PM -0700, Axel Rasmussen wrote:

[...]

@@ -1820,16 +1821,27 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, page = pagecache_get_page(mapping, index, FGP_ENTRY | FGP_HEAD | FGP_LOCK, 0);

• if (xa_is_value(page)) {

• swapped = xa_is_value(page);
• if (swapped) { error = shmem_swapin_page(inode, index, &page, sgp, gfp, vma, fault_type); if (error == -EEXIST) goto repeat;

• *pagep = page;

• return error;
  

• if (error)
  

• 	return error;
  

  }

• if (page && vma && userfaultfd_minor(vma)) {

• unlock_page(page);
  

• put_page(page);
  

• *fault_type = handle_userfault(vmf, VM_UFFD_MINOR);
  

• return 0;
  

• }

If we need to consider swapping for UFFDIO_CONTINUE later (as Hugh pointed out previously, which looks the right thing to do), it's indeed a bit awkward to swapin here. Maybe move this chunk to right after pagecache_get_page() returns? Then no need to touch the rest.

• if (swapped)

• return 0;
  

• if (page) hindex = page->index; if (page && sgp == SGP_WRITE)

-- 2.31.1.295.g9ea45b61b8-goog