[PATCH v2 5/5] mm/filemap: Avoid retrying page faults on uptodate folios in filemap faults

[Barry Song (Xiaomi)]

For uptodate folios, we are not waiting on I/O. We should
be able to acquire the folio lock shortly, so there is no
need to drop per-vma locks and perform a full PF retry.

Signed-off-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
---
 mm/filemap.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index b532d6cbafc8..0d2f6af5d0fe 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3533,6 +3533,13 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 		}
 	}
 
+	/*
+	 * If the folio is uptodate, we are likely only waiting for
+	 * another concurrent PTE mapping to complete, which should
+	 * be brief. No need to drop the lock and retry the fault.
+	 */
+	if (folio_test_uptodate(folio))
+		vmf->flags &= ~FAULT_FLAG_ALLOW_RETRY;
 	if (!lock_folio_maybe_drop_mmap(vmf, folio, &fpin))
 		goto out_retry;
 
-- 
2.39.3 (Apple Git-146)