From 80cdbb01f3a3e08cfe11078e2cd2f226351b0bce Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh@NetBSD.org>
Date: Fri, 21 Feb 2020 23:17:33 +0000
Subject: [PATCH] WIP: lfs write flushbehind, like ffs does.

This is tuned to the lfs segment size.  It's kind of wrong because we
really want to start flushing when the file system as a whole has
accrued a segment's worth of data -- not just when a single file has.
Writing a large number of little files won't trigger this.

Currently WIP because it breaks tests/fs/vfs/t_full.
---
 sys/ufs/lfs/ulfs_readwrite.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/sys/ufs/lfs/ulfs_readwrite.c b/sys/ufs/lfs/ulfs_readwrite.c
index 12984c77a04f..01805dd18e4f 100644
--- a/sys/ufs/lfs/ulfs_readwrite.c
+++ b/sys/ufs/lfs/ulfs_readwrite.c
@@ -35,6 +35,8 @@
 #include <sys/cdefs.h>
 __KERNEL_RCSID(1, "$NetBSD: ulfs_readwrite.c,v 1.25 2019/06/20 00:49:11 christos Exp $");
 
+#include <sys/bitops.h>
+
 #define	FS			struct lfs
 #define	I_FS			i_lfs
 #define	READ			lfs_read
@@ -278,7 +280,6 @@ WRITE(void *v)
 
 	KASSERT(vp->v_type == VREG);
 
-	async = true;
 	lfs_availwait(fs, lfs_btofsb(fs, uio->uio_resid));
 	lfs_check(vp, LFS_UNUSED_LBN, 0);
 
@@ -395,7 +396,16 @@ WRITE(void *v)
 		 * XXXUBC simplistic async flushing.
 		 */
 
-		__USE(async);
+		unsigned shift = ilog2(lfs_segsize(fs)) - 1;
+		if (!async &&
+		    (oldoff >> shift) != (uio->uio_offset >> shift)) {
+			mutex_enter(vp->v_interlock);
+			error = VOP_PUTPAGES(vp, (oldoff >> shift) << shift,
+			    (uio->uio_offset >> shift) << shift,
+			    PGO_CLEANIT | PGO_LAZY);
+			if (error)
+				break;
+		}
 	}
 	if (error == 0 && ioflag & IO_SYNC) {
 		mutex_enter(vp->v_interlock);