When fsync'ing a file on a filesystem using soft updates, we first try

to write all the dirty blocks. If some of those blocks have dependencies,
they will be remarked dirty when the I/O completes. On systems with
really fast I/O systems, it is possible to get in an infinite loop trying
to flush the buffers, because the I/O finishes before we can get all the
dirty buffers off the v_dirtyblkhd list and into the I/O queue. (The
previous algorithm looped over the v_dirtyblkhd list writing out buffers
until the list emptied.) So, now we mark each buffer that we try to
write so that we can distinguish the ones that are being remarked dirty
from those that we have not yet tried to flush. Once we have tried to
push every buffer once, we then push any associated metadata that is
causing the remaining buffers to be redirtied.

Submitted by:	Matthew Dillon <dillon@apollo.backplane.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/sys/bio.h b/sys/sys/bio.h
index 58b309b232e3..5ce4039ce904 100644
--- a/sys/sys/bio.h
+++ b/sys/sys/bio.h
@@ -36,7 +36,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)buf.h	8.9 (Berkeley) 3/30/95
- * $Id: buf.h,v 1.62 1999/01/21 08:29:08 dillon Exp $
+ * $Id: buf.h,v 1.63 1999/01/21 13:41:12 peter Exp $
  */
 
 #ifndef _SYS_BUF_H_
@@ -164,7 +164,7 @@ struct buf {
 #define	B_DONE		0x00000200	/* I/O completed. */
 #define	B_EINTR		0x00000400	/* I/O was interrupted */
 #define	B_ERROR		0x00000800	/* I/O error occurred. */
-#define	B_AVAIL2	0x00001000	/* Available flag */
+#define	B_SCANNED	0x00001000	/* VOP_FSYNC funcs mark written bufs */
 #define	B_INVAL		0x00002000	/* Does not contain valid info. */
 #define	B_LOCKED	0x00004000	/* Locked in core (not reusable). */
 #define	B_NOCACHE	0x00008000	/* Do not cache block after use. */