xfs: cleanup mapping tmpfs folios into the buffer cache

Directly assign b_addr based on the tmpfs folios without a detour
through pages, reuse the folio_put path used for non-tmpfs buffers
and replace all references to pages in comments with folios.

Partially based on a patch from Dave Chinner <dchinner@redhat.com>.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

Author: Christoph Hellwig

fs/xfs/xfs_buf.c

@@ -206,9 +206,7 @@ xfs_buf_free(
 	if (!xfs_buftarg_is_mem(bp->b_target) && size >= PAGE_SIZE)
 		mm_account_reclaimed_pages(howmany(size, PAGE_SHIFT));
 
-	if (xfs_buftarg_is_mem(bp->b_target))
-		xmbuf_unmap_page(bp);
-	else if (is_vmalloc_addr(bp->b_addr))
+	if (is_vmalloc_addr(bp->b_addr))
 		vfree(bp->b_addr);
 	else if (bp->b_flags & _XBF_KMEM)
 		kfree(bp->b_addr);
@@ -275,7 +273,7 @@ xfs_buf_alloc_backing_mem(
 	struct folio	*folio;
 
 	if (xfs_buftarg_is_mem(bp->b_target))
-		return xmbuf_map_page(bp);
+		return xmbuf_map_backing_mem(bp);
 
 	/* Assure zeroed buffer for non-read cases. */
 	if (!(flags & XBF_READ))

fs/xfs/xfs_buf_mem.c

@@ -74,7 +74,7 @@ xmbuf_alloc(
 
 	/*
 	 * We don't want to bother with kmapping data during repair, so don't
-	 * allow highmem pages to back this mapping.
+	 * allow highmem folios to back this mapping.
 	 */
 	mapping_set_gfp_mask(inode->i_mapping, GFP_KERNEL);
 
@@ -127,14 +127,13 @@ xmbuf_free(
 	kfree(btp);
 }
 
-/* Directly map a shmem page into the buffer cache. */
+/* Directly map a shmem folio into the buffer cache. */
 int
-xmbuf_map_page(
+xmbuf_map_backing_mem(
 	struct xfs_buf		*bp)
 {
 	struct inode		*inode = file_inode(bp->b_target->bt_file);
 	struct folio		*folio = NULL;
-	struct page		*page;
 	loff_t                  pos = BBTOB(xfs_buf_daddr(bp));
 	int			error;
 
@@ -159,30 +158,17 @@ xmbuf_map_page(
 		return -EIO;
 	}
 
-	page = folio_file_page(folio, pos >> PAGE_SHIFT);
-
 	/*
-	 * Mark the page dirty so that it won't be reclaimed once we drop the
-	 * (potentially last) reference in xmbuf_unmap_page.
+	 * Mark the folio dirty so that it won't be reclaimed once we drop the
+	 * (potentially last) reference in xfs_buf_free.
 	 */
-	set_page_dirty(page);
-	unlock_page(page);
+	folio_set_dirty(folio);
+	folio_unlock(folio);
 
-	bp->b_addr = page_address(page);
+	bp->b_addr = folio_address(folio);
 	return 0;
 }
 
-/* Unmap a shmem page that was mapped into the buffer cache. */
-void
-xmbuf_unmap_page(
-	struct xfs_buf		*bp)
-{
-	ASSERT(xfs_buftarg_is_mem(bp->b_target));
-
-	put_page(virt_to_page(bp->b_addr));
-	bp->b_addr = NULL;
-}
-
 /* Is this a valid daddr within the buftarg? */
 bool
 xmbuf_verify_daddr(
@@ -196,7 +182,7 @@ xmbuf_verify_daddr(
 	return daddr < (inode->i_sb->s_maxbytes >> BBSHIFT);
 }
 
-/* Discard the page backing this buffer. */
+/* Discard the folio backing this buffer. */
 static void
 xmbuf_stale(
 	struct xfs_buf		*bp)
@@ -211,7 +197,7 @@ xmbuf_stale(
 }
 
 /*
- * Finalize a buffer -- discard the backing page if it's stale, or run the
+ * Finalize a buffer -- discard the backing folio if it's stale, or run the
  * write verifier to detect problems.
  */
 int

fs/xfs/xfs_buf_mem.h

@@ -19,16 +19,14 @@ int xmbuf_alloc(struct xfs_mount *mp, const char *descr,
 		struct xfs_buftarg **btpp);
 void xmbuf_free(struct xfs_buftarg *btp);
 
-int xmbuf_map_page(struct xfs_buf *bp);
-void xmbuf_unmap_page(struct xfs_buf *bp);
 bool xmbuf_verify_daddr(struct xfs_buftarg *btp, xfs_daddr_t daddr);
 void xmbuf_trans_bdetach(struct xfs_trans *tp, struct xfs_buf *bp);
 int xmbuf_finalize(struct xfs_buf *bp);
 #else
 # define xfs_buftarg_is_mem(...)	(false)
-# define xmbuf_map_page(...)		(-ENOMEM)
-# define xmbuf_unmap_page(...)		((void)0)
 # define xmbuf_verify_daddr(...)	(false)
 #endif /* CONFIG_XFS_MEMORY_BUFS */
 
+int xmbuf_map_backing_mem(struct xfs_buf *bp);
+
 #endif /* __XFS_BUF_MEM_H__ */