From 3b9e4e18a6045688c5980322a34b3085ccf120a0 Mon Sep 17 00:00:00 2001
From: mpi <mpi@openbsd.org>
Date: Tue, 28 Jun 2022 10:38:55 +0000
Subject: [PATCH] Do not consider adjacent pages when doing a CoW.

Those pages should already be entered, this speeds up CoW faults.

Stolen from NetBSD.

ok miod@, kettenis@
---
 sys/uvm/uvm_fault.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/sys/uvm/uvm_fault.c b/sys/uvm/uvm_fault.c
index 56a30dc9ff8..ff4fb28f51f 100644
--- a/sys/uvm/uvm_fault.c
+++ b/sys/uvm/uvm_fault.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_fault.c,v 1.129 2022/04/04 09:27:05 kettenis Exp $	*/
+/*	$OpenBSD: uvm_fault.c,v 1.130 2022/06/28 10:38:55 mpi Exp $	*/
 /*	$NetBSD: uvm_fault.c,v 1.51 2000/08/06 00:22:53 thorpej Exp $	*/
 
 /*
@@ -736,6 +736,16 @@ uvm_fault_check(struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
 		return EFAULT;
 	}
 
+	/*
+	 * for a case 2B fault waste no time on adjacent pages because
+	 * they are likely already entered.
+	 */
+	if (uobj != NULL && amap != NULL &&
+	    (flt->access_type & PROT_WRITE) != 0) {
+		/* wide fault (!narrow) */
+		flt->narrow = TRUE;
+	}
+
 	/*
 	 * establish range of interest based on advice from mapper
 	 * and then clip to fit map entry.   note that we only want
-- 
2.20.1