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The vfs.write_behind sysctl and related code support has been added to

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allow changes to the filesystem's write_behind behavior.  By the
default the filesystem aggressively issues write_behind's.  Three values
may be specified for vfs.write_behind.  0 disables write_behind, 1 results
in historical operation (agressive write_behind), and 2 is an experimental
backed-off write_behind.  The values of 0 and 1 are recommended.  The value
of 0 is recommended in conjuction with an increase in the number of
NBUF's and the number of dirty buffers allowed (vfs.{lo,hi}dirtybuffers).
Note that a value of 0 will radically increase the dirty buffer load on
the system.  Future work on write_behind behavior will use values 2 and
greater for testing purposes.

Submitted by:	Matthew Dillon <dillon@apollo.backplane.com>
Reviewed by:	Kirk McKusick <mckusick@mckusick.com>
This commit is contained in:
Kirk McKusick 1999-07-04 00:31:17 +00:00
parent e929c00d23
commit 1c9ca5858f
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=48545
1 changed files with 40 additions and 3 deletions
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43
sys/kern/vfs_cluster.c
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@ -33,7 +33,7 @@
* SUCH DAMAGE.
*
* @(#)vfs_cluster.c 8.7 (Berkeley) 2/13/94
* $Id: vfs_cluster.c,v 1.84 1999/06/26 02:46:08 mckusick Exp $
* $Id: vfs_cluster.c,v 1.85 1999/06/29 05:59:43 peter Exp $
*/
#include "opt_debug_cluster.h"
@ -51,6 +51,7 @@
#include <vm/vm_prot.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <sys/sysctl.h>
#if defined(CLUSTERDEBUG)
#include <sys/sysctl.h>
@ -66,6 +67,9 @@ static struct buf *
cluster_rbuild __P((struct vnode *vp, u_quad_t filesize, daddr_t lbn,
daddr_t blkno, long size, int run, struct buf *fbp));
static int write_behind = 1;
SYSCTL_INT(_vfs, OID_AUTO, write_behind, CTLFLAG_RW, &write_behind, 0, "");
extern vm_page_t bogus_page;
extern int cluster_pbuf_freecnt;
@ -153,12 +157,14 @@ cluster_read(vp, filesize, lblkno, size, cred, totread, seqcount, bpp)
(i == (maxra - 1)))
tbp->b_flags |= B_RAM;
#if 0
if ((tbp->b_usecount < 1) &&
BUF_REFCNT(tbp) == 0 &&
(tbp->b_qindex == QUEUE_LRU)) {
TAILQ_REMOVE(&bufqueues[QUEUE_LRU], tbp, b_freelist);
TAILQ_INSERT_TAIL(&bufqueues[QUEUE_LRU], tbp, b_freelist);
}
#endif
}
splx(s);
if (i >= maxra) {
@ -494,6 +500,37 @@ cluster_callback(bp)
relpbuf(bp, &cluster_pbuf_freecnt);
}
/*
* cluster_wbuild_wb:
*
* Implement modified write build for cluster.
*
* write_behind = 0 write behind disabled
* write_behind = 1 write behind normal (default)
* write_behind = 2 write behind backed-off
*/
static __inline int
cluster_wbuild_wb(struct vnode *vp, long size, daddr_t start_lbn, int len)
{
int r = 0;
switch(write_behind) {
case 2:
if (start_lbn < len)
break;
start_lbn -= len;
/* fall through */
case 1:
r = cluster_wbuild(vp, size, start_lbn, len);
/* fall through */
default:
/* fall through */
break;
}
return(r);
}
/*
* Do clustered write for FFS.
*
@ -566,7 +603,7 @@ cluster_write(bp, filesize)
bpp < endbp; bpp++)
brelse(*bpp);
free(buflist, M_SEGMENT);
cluster_wbuild(vp, lblocksize,
cluster_wbuild_wb(vp, lblocksize,
vp->v_cstart, cursize);
} else {
/*
@ -612,7 +649,7 @@ cluster_write(bp, filesize)
* At end of cluster, write it out.
*/
bdwrite(bp);
cluster_wbuild(vp, lblocksize, vp->v_cstart, vp->v_clen + 1);
cluster_wbuild_wb(vp, lblocksize, vp->v_cstart, vp->v_clen + 1);
vp->v_clen = 0;
vp->v_cstart = lbn + 1;
} else