[PATCH 13/15] xfs: don't unconditionally allocate a new page in xfile_get_page

[Christoph Hellwig <hch@xxxxxx>]

Pass a flags argument to xfile_get_page, and only allocate a new page
if the XFILE_ALLOC flag is passed.  This allows to also use
xfile_get_page for pure readers that do not want to allocate a new
page or dirty the existing one.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 fs/xfs/scrub/xfarray.c |  2 +-
 fs/xfs/scrub/xfile.c   | 14 ++++++++++----
 fs/xfs/scrub/xfile.h   |  4 +++-
 3 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/scrub/xfarray.c b/fs/xfs/scrub/xfarray.c
index 4f396462186793..8543067d46366d 100644
--- a/fs/xfs/scrub/xfarray.c
+++ b/fs/xfs/scrub/xfarray.c
@@ -572,7 +572,7 @@ xfarray_sort_get_page(
 {
 	struct page		*page;
 
-	page = xfile_get_page(si->array->xfile, pos, len);
+	page = xfile_get_page(si->array->xfile, pos, len, XFILE_ALLOC);
 	if (IS_ERR(page))
 		return PTR_ERR(page);
 	si->page = page;
diff --git a/fs/xfs/scrub/xfile.c b/fs/xfs/scrub/xfile.c
index 715c4d10b67c14..3ed7fb82a4497b 100644
--- a/fs/xfs/scrub/xfile.c
+++ b/fs/xfs/scrub/xfile.c
@@ -274,7 +274,8 @@ struct page *
 xfile_get_page(
 	struct xfile		*xf,
 	loff_t			pos,
-	unsigned int		len)
+	unsigned int		len,
+	unsigned int		flags)
 {
 	struct inode		*inode = file_inode(xf->file);
 	struct folio		*folio = NULL;
@@ -293,15 +294,19 @@ xfile_get_page(
 	 * Increase the file size first so that shmem_get_folio(..., SGP_CACHE),
 	 * actually allocates a folio instead of erroring out.
 	 */
-	if (pos + len > i_size_read(inode))
+	if ((flags & XFILE_ALLOC) && pos + len > i_size_read(inode))
 		i_size_write(inode, pos + len);
 
 	pflags = memalloc_nofs_save();
-	error = shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio, SGP_CACHE);
+	error = shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
+			(flags & XFILE_ALLOC) ? SGP_CACHE : SGP_READ);
 	memalloc_nofs_restore(pflags);
 	if (error)
 		return ERR_PTR(error);
 
+	if (!folio)
+		return NULL;
+
 	page = folio_file_page(folio, pos >> PAGE_SHIFT);
 	if (PageHWPoison(page)) {
 		folio_put(folio);
@@ -312,7 +317,8 @@ xfile_get_page(
 	 * Mark the page dirty so that it won't be reclaimed once we drop the
 	 * (potentially last) reference in xfile_put_page.
 	 */
-	set_page_dirty(page);
+	if (flags & XFILE_ALLOC)
+		set_page_dirty(page);
 	return page;
 }
 
diff --git a/fs/xfs/scrub/xfile.h b/fs/xfs/scrub/xfile.h
index 993368b37b4b7c..f0403ea869e4d0 100644
--- a/fs/xfs/scrub/xfile.h
+++ b/fs/xfs/scrub/xfile.h
@@ -19,7 +19,9 @@ int xfile_obj_store(struct xfile *xf, const void *buf, size_t count,
 
 loff_t xfile_seek_data(struct xfile *xf, loff_t pos);
 
-struct page *xfile_get_page(struct xfile *xf, loff_t offset, unsigned int len);
+#define XFILE_ALLOC		(1 << 0) /* allocate page if not present */
+struct page *xfile_get_page(struct xfile *xf, loff_t offset, unsigned int len,
+		unsigned int flags);
 void xfile_put_page(struct xfile *xf, struct page *page);
 
 #endif /* __XFS_SCRUB_XFILE_H__ */
-- 
2.39.2