From b49d824e8bc1df3bef3e72a9f2ddcc59a8b72ef0 Mon Sep 17 00:00:00 2001
From: Mike Silbersack <silby@FreeBSD.org>
Date: Sun, 8 Feb 2004 07:35:48 +0000
Subject: [PATCH] Add the SF_NODISKIO flag to sendfile.  This flag causes
 sendfile to be mindful of blocking on disk I/O and instead return EBUSY when
 such blocking would occur.

Results from the DeBox project indicate that blocking on disk I/O
can slow the performance of a kqueue/poll based webserver.  Using
a flag such as SF_NODISKIO and throwing connections that would block
to helper processes/threads helped increase performance.

Currently, only the Flash webserver uses this flag, although it could
probably be applied to thttpd with relative ease.

Idea by:	Yaoping Ruan & Vivek Pai
---
 sys/kern/uipc_syscalls.c | 41 +++++++++++++++++++++-------------------
 sys/sys/socket.h         |  5 +++++
 2 files changed, 27 insertions(+), 19 deletions(-)

diff --git a/sys/kern/uipc_syscalls.c b/sys/kern/uipc_syscalls.c
index 55f588f20667..28ee96438379 100644
--- a/sys/kern/uipc_syscalls.c
+++ b/sys/kern/uipc_syscalls.c
@@ -1836,7 +1836,11 @@ retry_lookup:
 		 * If page is not valid for what we need, initiate I/O
 		 */
 
-		if (!pg->valid || !vm_page_is_valid(pg, pgoff, xfsize)) {
+		if (pg->valid && vm_page_is_valid(pg, pgoff, xfsize)) {
+			VM_OBJECT_UNLOCK(obj);
+		} else if (uap->flags & SF_NODISKIO) {
+			error = EBUSY;
+		} else {
 			int bsize, resid;
 
 			/*
@@ -1867,26 +1871,25 @@ retry_lookup:
 			vm_page_lock_queues();
 			vm_page_flag_clear(pg, PG_ZERO);
 			vm_page_io_finish(pg);
-			if (error) {
-				vm_page_unwire(pg, 0);
-				/*
-				 * See if anyone else might know about this page.
-				 * If not and it is not valid, then free it.
-				 */
-				if (pg->wire_count == 0 && pg->valid == 0 &&
-				    pg->busy == 0 && !(pg->flags & PG_BUSY) &&
-				    pg->hold_count == 0) {
-					vm_page_busy(pg);
-					vm_page_free(pg);
-				}
-				vm_page_unlock_queues();
-				VM_OBJECT_UNLOCK(obj);
-				sbunlock(&so->so_snd);
-				goto done;
-			}
 			mbstat.sf_iocnt++;
-		} else {
+		}
+	
+		if (error) {
+			vm_page_unwire(pg, 0);
+			/*
+			 * See if anyone else might know about this page.
+			 * If not and it is not valid, then free it.
+			 */
+			if (pg->wire_count == 0 && pg->valid == 0 &&
+			    pg->busy == 0 && !(pg->flags & PG_BUSY) &&
+			    pg->hold_count == 0) {
+				vm_page_busy(pg);
+				vm_page_free(pg);
+			}
+			vm_page_unlock_queues();
 			VM_OBJECT_UNLOCK(obj);
+			sbunlock(&so->so_snd);
+			goto done;
 		}
 		vm_page_unlock_queues();
 
diff --git a/sys/sys/socket.h b/sys/sys/socket.h
index 34865fd81a60..4acff20544de 100644
--- a/sys/sys/socket.h
+++ b/sys/sys/socket.h
@@ -505,6 +505,11 @@ struct sf_hdtr {
 	struct iovec *trailers;	/* pointer to an array of trailer struct iovec's */
 	int trl_cnt;		/* number of trailer iovec's */
 };
+
+/*
+ * Sendfile-specific flag(s)
+ */
+#define        SF_NODISKIO     0x00000001
 #endif
 
 #ifndef	_KERNEL