[PATCH v3 1/3] tmpfs: factor out folio zeroing logic at writeout time

[Brian Foster <bfoster@redhat.com>]

tmpfs currently zeroes !uptodate folios at shmem_writeout() time to
ensure they are zeroed in swap. We want to expand this behavior to zero
post-eof ranges to better abide POSIX file extension requirements. As a
first step, split out the existing zeroing code into a separate block.
No functional changes in this patch.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 mm/shmem.c | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 0a25ee095b86..651602460770 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1626,22 +1626,23 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
 	 * good idea to continue anyway, once we're pushing into swap.  So
 	 * reactivate the folio, and let shmem_fallocate() quit when too many.
 	 */
+	if (!folio_test_uptodate(folio) && inode->i_private) {
+		struct shmem_falloc *shmem_falloc;
+		spin_lock(&inode->i_lock);
+		shmem_falloc = inode->i_private;
+		if (shmem_falloc &&
+		    !shmem_falloc->waitq &&
+		    index >= shmem_falloc->start &&
+		    index < shmem_falloc->next)
+			shmem_falloc->nr_unswapped += nr_pages;
+		else
+			shmem_falloc = NULL;
+		spin_unlock(&inode->i_lock);
+		if (shmem_falloc)
+			goto redirty;
+	}
+
 	if (!folio_test_uptodate(folio)) {
-		if (inode->i_private) {
-			struct shmem_falloc *shmem_falloc;
-			spin_lock(&inode->i_lock);
-			shmem_falloc = inode->i_private;
-			if (shmem_falloc &&
-			    !shmem_falloc->waitq &&
-			    index >= shmem_falloc->start &&
-			    index < shmem_falloc->next)
-				shmem_falloc->nr_unswapped += nr_pages;
-			else
-				shmem_falloc = NULL;
-			spin_unlock(&inode->i_lock);
-			if (shmem_falloc)
-				goto redirty;
-		}
 		folio_zero_range(folio, 0, folio_size(folio));
 		flush_dcache_folio(folio);
 		folio_mark_uptodate(folio);
-- 
2.51.1