ceph: Convert ceph_find_incompatible() to take a folio

Both callers already have the folio.  Pass it in and use it throughout.
Removes some hidden calls to compound_head() and a reference to
page->mapping.

Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Link: https://lore.kernel.org/r/20250217185119.430193-4-willy@infradead.org
Tested-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Matthew Wilcox (Oracle)

fs/ceph/addr.c

@@ -1771,56 +1771,56 @@ static int context_is_writeable_or_written(struct inode *inode,
 
 /**
  * ceph_find_incompatible - find an incompatible context and return it
- * @page: page being dirtied
+ * @folio: folio being dirtied
  *
- * We are only allowed to write into/dirty a page if the page is
+ * We are only allowed to write into/dirty a folio if the folio is
  * clean, or already dirty within the same snap context. Returns a
  * conflicting context if there is one, NULL if there isn't, or a
  * negative error code on other errors.
  *
- * Must be called with page lock held.
+ * Must be called with folio lock held.
  */
 static struct ceph_snap_context *
-ceph_find_incompatible(struct page *page)
+ceph_find_incompatible(struct folio *folio)
 {
-	struct inode *inode = page->mapping->host;
+	struct inode *inode = folio->mapping->host;
 	struct ceph_client *cl = ceph_inode_to_client(inode);
 	struct ceph_inode_info *ci = ceph_inode(inode);
 
 	if (ceph_inode_is_shutdown(inode)) {
-		doutc(cl, " %llx.%llx page %p is shutdown\n",
-		      ceph_vinop(inode), page);
+		doutc(cl, " %llx.%llx folio %p is shutdown\n",
+		      ceph_vinop(inode), folio);
 		return ERR_PTR(-ESTALE);
 	}
 
 	for (;;) {
 		struct ceph_snap_context *snapc, *oldest;
 
-		wait_on_page_writeback(page);
+		folio_wait_writeback(folio);
 
-		snapc = page_snap_context(page);
+		snapc = page_snap_context(&folio->page);
 		if (!snapc || snapc == ci->i_head_snapc)
 			break;
 
 		/*
-		 * this page is already dirty in another (older) snap
+		 * this folio is already dirty in another (older) snap
 		 * context!  is it writeable now?
 		 */
 		oldest = get_oldest_context(inode, NULL, NULL);
 		if (snapc->seq > oldest->seq) {
 			/* not writeable -- return it for the caller to deal with */
 			ceph_put_snap_context(oldest);
-			doutc(cl, " %llx.%llx page %p snapc %p not current or oldest\n",
-			      ceph_vinop(inode), page, snapc);
+			doutc(cl, " %llx.%llx folio %p snapc %p not current or oldest\n",
+			      ceph_vinop(inode), folio, snapc);
 			return ceph_get_snap_context(snapc);
 		}
 		ceph_put_snap_context(oldest);
 
-		/* yay, writeable, do it now (without dropping page lock) */
-		doutc(cl, " %llx.%llx page %p snapc %p not current, but oldest\n",
-		      ceph_vinop(inode), page, snapc);
-		if (clear_page_dirty_for_io(page)) {
-			int r = writepage_nounlock(page, NULL);
+		/* yay, writeable, do it now (without dropping folio lock) */
+		doutc(cl, " %llx.%llx folio %p snapc %p not current, but oldest\n",
+		      ceph_vinop(inode), folio, snapc);
+		if (folio_clear_dirty_for_io(folio)) {
+			int r = writepage_nounlock(&folio->page, NULL);
 			if (r < 0)
 				return ERR_PTR(r);
 		}
@@ -1835,7 +1835,7 @@ static int ceph_netfs_check_write_begin(struct file *file, loff_t pos, unsigned
 	struct ceph_inode_info *ci = ceph_inode(inode);
 	struct ceph_snap_context *snapc;
 
-	snapc = ceph_find_incompatible(folio_page(*foliop, 0));
+	snapc = ceph_find_incompatible(*foliop);
 	if (snapc) {
 		int r;
 
@@ -2095,7 +2095,7 @@ static vm_fault_t ceph_page_mkwrite(struct vm_fault *vmf)
 			break;
 		}
 
-		snapc = ceph_find_incompatible(&folio->page);
+		snapc = ceph_find_incompatible(folio);
 		if (!snapc) {
 			/* success.  we'll keep the folio locked. */
 			folio_mark_dirty(folio);