Matthew Wilcox (Oracle) [off-list ref] wrote:

 /**
- * set_page_fscache - Set PG_fscache on a page and take a ref
- * @page: The page.
+ * folio_start_fscache - Start an fscache operation on a folio.
+ * @folio: The folio.
  *
- * Set the PG_fscache (PG_private_2) flag on a page and take the reference
- * needed for the VM to handle its lifetime correctly.  This sets the flag and
- * takes the reference unconditionally, so care must be taken not to set the
- * flag again if it's already set.
+ * Call this function before an fscache operation starts on a folio.
+ * Starting a second fscache operation before the first one finishes is
+ * not allowed.

That's not correct.  It's only used for operations that write from the page to
disk.  Operations that read into the page are covered by the page lock.

+ * folio_end_fscache - End an fscache operation on a folio.
...
+ * Call this function after an fscache operation has finished.  This will
+ * wake any sleepers waiting on this folio.

Ditto.

+ * folio_wait_fscache - Wait for an fscache operation on this folio to end.
+ * @folio: The folio.
  *
+ * If an fscache operation is in progress on this folio, wait for it to
+ * finish.  Another fscache operation may start after this one finishes,
+ * unless the caller holds the folio lock.

Ditto.

Apart from that, it looks okay.

David