Fix stack dsl_scan_visitbp()

To reduce stack overhead this topic branch moves the 128 byte
blkptr_t data strucutre in dsl_scan_visitbp() to the heap.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

diff --git a/module/zfs/dsl_scan.c b/module/zfs/dsl_scan.c
index e18dadf..525832b 100644 (file)
--- a/module/zfs/dsl_scan.c
+++ b/module/zfs/dsl_scan.c
@@ -792,18 +792,21 @@ dsl_scan_visitbp(blkptr_t *bp, const zbookmark_t *zb,
 {
        dsl_pool_t *dp = scn->scn_dp;
        arc_buf_t *buf = NULL;
-       blkptr_t bp_toread = *bp;
+       blkptr_t *bp_toread;
+
+       bp_toread = kmem_alloc(sizeof (blkptr_t), KM_SLEEP);
+       *bp_toread = *bp;
 
        /* ASSERT(pbuf == NULL || arc_released(pbuf)); */
 
        if (dsl_scan_check_pause(scn, zb))
-               return;
+               goto out;
 
        if (dsl_scan_check_resume(scn, dnp, zb))
-               return;
+               goto out;
 
        if (bp->blk_birth == 0)
-               return;
+               goto out;
 
        scn->scn_visited_this_txg++;
 
@@ -814,7 +817,7 @@ dsl_scan_visitbp(blkptr_t *bp, const zbookmark_t *zb,
            pbuf, bp);
 
        if (bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
-               return;
+               goto out;
 
        if (BP_GET_TYPE(bp) != DMU_OT_USERGROUP_USED) {
                /*
@@ -829,12 +832,12 @@ dsl_scan_visitbp(blkptr_t *bp, const zbookmark_t *zb,
                 * it (original untranslated -> translations from
                 * deleted snap -> now).
                 */
-               bp_toread = *bp;
+               *bp_toread = *bp;
        }
 
-       if (dsl_scan_recurse(scn, ds, ostype, dnp, &bp_toread, zb, tx,
+       if (dsl_scan_recurse(scn, ds, ostype, dnp, bp_toread, zb, tx,
            &buf) != 0)
-               return;
+               goto out;
 
        /*
         * If dsl_scan_ddt() has aready visited this block, it will have
@@ -844,7 +847,7 @@ dsl_scan_visitbp(blkptr_t *bp, const zbookmark_t *zb,
        if (ddt_class_contains(dp->dp_spa,
            scn->scn_phys.scn_ddt_class_max, bp)) {
                ASSERT(buf == NULL);
-               return;
+               goto out;
        }
 
        /*
@@ -859,6 +862,8 @@ dsl_scan_visitbp(blkptr_t *bp, const zbookmark_t *zb,
        }
        if (buf)
                (void) arc_buf_remove_ref(buf, &buf);
+out:
+       kmem_free(bp_toread, sizeof(blkptr_t));
 }
 
 static void