try_get_folio() takes in a page, then chooses to do some folio
operations based on the flags (either FOLL_GET or FOLL_PIN).
We can rewrite this function to be more purpose oriented.
After calling try_get_folio(), if neither FOLL_GET nor FOLL_PIN are set,
warn and fail. If FOLL_GET is set we can return the result. If FOLL_GET
is not set then FOLL_PIN is set, so we pin the folio.
This change assists with folio conversions, and makes the function more
readable.
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
---
mm/gup.c | 86 ++++++++++++++++++++++++++++----------------------------
1 file changed, 43 insertions(+), 43 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index bbe416236593..6ec5c9629dc9 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -123,58 +123,58 @@ static inline struct folio *try_get_folio(struct page *page, int refs)
*/
struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags)
{
+ struct folio *folio;
+
+ if (WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == 0))
+ return NULL;
+
if (unlikely(!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(page)))
return NULL;
- if (flags & FOLL_GET)
- return try_get_folio(page, refs);
- else if (flags & FOLL_PIN) {
- struct folio *folio;
+ folio = try_get_folio(page, refs);
- /*
- * Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a
- * right zone, so fail and let the caller fall back to the slow
- * path.
- */
- if (unlikely((flags & FOLL_LONGTERM) &&
- !is_longterm_pinnable_page(page)))
- return NULL;
+ if (flags & FOLL_GET)
+ return folio;
- /*
- * CAUTION: Don't use compound_head() on the page before this
- * point, the result won't be stable.
- */
- folio = try_get_folio(page, refs);
- if (!folio)
- return NULL;
+ /* FOLL_PIN is set */
+ if (!folio)
+ return NULL;
- /*
- * When pinning a large folio, use an exact count to track it.
- *
- * However, be sure to *also* increment the normal folio
- * refcount field at least once, so that the folio really
- * is pinned. That's why the refcount from the earlier
- * try_get_folio() is left intact.
- */
- if (folio_test_large(folio))
- atomic_add(refs, &folio->_pincount);
- else
- folio_ref_add(folio,
- refs * (GUP_PIN_COUNTING_BIAS - 1));
- /*
- * Adjust the pincount before re-checking the PTE for changes.
- * This is essentially a smp_mb() and is paired with a memory
- * barrier in page_try_share_anon_rmap().
- */
- smp_mb__after_atomic();
+ /*
+ * Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a
+ * right zone, so fail and let the caller fall back to the slow
+ * path.
+ */
+ if (unlikely((flags & FOLL_LONGTERM) &&
+ !folio_is_longterm_pinnable(folio))) {
+ if (!put_devmap_managed_page_refs(&folio->page, refs))
+ folio_put_refs(folio, refs);
+ return NULL;
+ }
- node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, refs);
+ /*
+ * When pinning a large folio, use an exact count to track it.
+ *
+ * However, be sure to *also* increment the normal folio
+ * refcount field at least once, so that the folio really
+ * is pinned. That's why the refcount from the earlier
+ * try_get_folio() is left intact.
+ */
+ if (folio_test_large(folio))
+ atomic_add(refs, &folio->_pincount);
+ else
+ folio_ref_add(folio,
+ refs * (GUP_PIN_COUNTING_BIAS - 1));
+ /*
+ * Adjust the pincount before re-checking the PTE for changes.
+ * This is essentially a smp_mb() and is paired with a memory
+ * barrier in page_try_share_anon_rmap().
+ */
+ smp_mb__after_atomic();
- return folio;
- }
+ node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, refs);
- WARN_ON_ONCE(1);
- return NULL;
+ return folio;
}
static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
--
2.40.1
