missed clustering for small block sizes in cluster_wbuild()

[Konstantin Belousov]

On Fri, Jun 07, 2013 at 05:28:11AM +1000, Bruce Evans wrote:
> I think this is best fixed be fixed by removing the check above and
> checking here.  Then back out of the changes.  I don't know this code
> well enough to write the backing out easily.

Could you test this, please ?

diff --git a/sys/kern/vfs_cluster.c b/sys/kern/vfs_cluster.c
index b280317..9e1528e 100644
--- a/sys/kern/vfs_cluster.c
+++ b/sys/kern/vfs_cluster.c
@@ -766,7 +766,7 @@ cluster_wbuild(struct vnode *vp, long size, daddr_t start_lbn, int len,
 {
 	struct buf *bp, *tbp;
 	struct bufobj *bo;
-	int i, j;
+	int i, j, jj;
 	int totalwritten = 0;
 	int dbsize = btodb(size);
 
@@ -904,14 +904,10 @@ cluster_wbuild(struct vnode *vp, long size, daddr_t start_lbn, int len,
 
 				/*
 				 * Check that the combined cluster
-				 * would make sense with regard to pages
-				 * and would not be too large
+				 * would make sense with regard to pages.
 				 */
-				if ((tbp->b_bcount != size) ||
-				  ((bp->b_blkno + (dbsize * i)) !=
-				    tbp->b_blkno) ||
-				  ((tbp->b_npages + bp->b_npages) >
-				    (vp->v_mount->mnt_iosize_max / PAGE_SIZE))) {
+				if (tbp->b_bcount != size ||
+				    bp->b_blkno + dbsize * i != tbp->b_blkno) {
 					BUF_UNLOCK(tbp);
 					break;
 				}
@@ -964,6 +960,22 @@ cluster_wbuild(struct vnode *vp, long size, daddr_t start_lbn, int len,
 						bp->b_pages[bp->b_npages] = m;
 						bp->b_npages++;
 					}
+					if (bp->b_npages > vp->v_mount->
+					    mnt_iosize_max / PAGE_SIZE) {
+						KASSERT(i != 0, ("XXX"));
+						j++;
+						for (jj = 0; jj < j; jj++) {
+							vm_page_io_finish(tbp->
+							    b_pages[jj]);
+						}
+						vm_object_pip_subtract(
+						    m->object, j);
+						bqrelse(tbp);
+						bp->b_npages -= j;
+						VM_OBJECT_WUNLOCK(tbp->
+						    b_bufobj->bo_object);
+						goto finishcluster;
+					}
 				}
 				VM_OBJECT_WUNLOCK(tbp->b_bufobj->bo_object);
 			}
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