[PATCH v2 4/5] mm: Don't retry page fault if folio is uptodate during swap-in

["Barry Song (Xiaomi)" <baohua@kernel.org>]

If we are waiting for long I/O to complete, it makes sense to
avoid holding locks for too long. However, if the folio is
uptodate, we are likely only waiting for a concurrent PTE
update to finish. Retrying the entire page fault seems
excessive.

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

diff --git a/mm/memory.c b/mm/memory.c
index 0c740ca363cc..a2e4f2d87ec8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4949,6 +4949,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	}
 
 	swapcache = folio;
+	/*
+	 * 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;
 	ret |= folio_lock_or_retry(folio, vmf);
 	if (ret & VM_FAULT_RETRY) {
 		if (fault_flag_allow_retry_first(vmf->flags) &&
-- 
2.39.3 (Apple Git-146)