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Conserve stack in dsl_scan_visit()

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The dsl_scan_visit() function is a little heavy weight taking 464
bytes on the stack.  This can be easily reduced for little cost by
moving zap_cursor_t and zap_attribute_t off the stack and on to the
heap.  After this change dsl_scan_visit() has been reduced in size
by 320 bytes.

This change was made to reduce stack usage in the dsl_scan_sync()
callpath which is recursive and has been observed to overflow the
stack.

Issue #174
This commit is contained in:
Brian Behlendorf 2011-04-26 14:56:04 -07:00
parent b81c4ac9af
commit 40a39e1103
1 changed files with 15 additions and 10 deletions
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25
module/zfs/dsl_scan.c
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@ -1328,8 +1328,8 @@ static void
dsl_scan_visit(dsl_scan_t *scn, dmu_tx_t *tx) dsl_scan_visit(dsl_scan_t *scn, dmu_tx_t *tx)
{ {
dsl_pool_t *dp = scn->scn_dp; dsl_pool_t *dp = scn->scn_dp;
zap_cursor_t zc; zap_cursor_t *zc;
zap_attribute_t za; zap_attribute_t *za;
if (scn->scn_phys.scn_ddt_bookmark.ddb_class <= if (scn->scn_phys.scn_ddt_bookmark.ddb_class <=
scn->scn_phys.scn_ddt_class_max) { scn->scn_phys.scn_ddt_class_max) {
@ -1377,24 +1377,26 @@ dsl_scan_visit(dsl_scan_t *scn, dmu_tx_t *tx)
* bookmark so we don't think that we're still trying to resume. * bookmark so we don't think that we're still trying to resume.
*/ */
bzero(&scn->scn_phys.scn_bookmark, sizeof (zbookmark_t)); bzero(&scn->scn_phys.scn_bookmark, sizeof (zbookmark_t));
zc = kmem_alloc(sizeof(zap_cursor_t), KM_SLEEP);
za = kmem_alloc(sizeof(zap_attribute_t), KM_SLEEP);
/* keep pulling things out of the zap-object-as-queue */ /* keep pulling things out of the zap-object-as-queue */
while (zap_cursor_init(&zc, dp->dp_meta_objset, while (zap_cursor_init(zc, dp->dp_meta_objset,
scn->scn_phys.scn_queue_obj), scn->scn_phys.scn_queue_obj),
zap_cursor_retrieve(&zc, &za) == 0) { zap_cursor_retrieve(zc, za) == 0) {
dsl_dataset_t *ds; dsl_dataset_t *ds;
uint64_t dsobj; uint64_t dsobj;
dsobj = strtonum(za.za_name, NULL); dsobj = strtonum(za->za_name, NULL);
VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset, VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
scn->scn_phys.scn_queue_obj, dsobj, tx)); scn->scn_phys.scn_queue_obj, dsobj, tx));
/* Set up min/max txg */ /* Set up min/max txg */
VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds)); VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
if (za.za_first_integer != 0) { if (za->za_first_integer != 0) {
scn->scn_phys.scn_cur_min_txg = scn->scn_phys.scn_cur_min_txg =
MAX(scn->scn_phys.scn_min_txg, MAX(scn->scn_phys.scn_min_txg,
za.za_first_integer); za->za_first_integer);
} else { } else {
scn->scn_phys.scn_cur_min_txg = scn->scn_phys.scn_cur_min_txg =
MAX(scn->scn_phys.scn_min_txg, MAX(scn->scn_phys.scn_min_txg,
@ -1404,11 +1406,14 @@ dsl_scan_visit(dsl_scan_t *scn, dmu_tx_t *tx)
dsl_dataset_rele(ds, FTAG); dsl_dataset_rele(ds, FTAG);
dsl_scan_visitds(scn, dsobj, tx); dsl_scan_visitds(scn, dsobj, tx);
zap_cursor_fini(&zc); zap_cursor_fini(zc);
if (scn->scn_pausing) if (scn->scn_pausing)
return; goto out;
} }
zap_cursor_fini(&zc); zap_cursor_fini(zc);
out:
kmem_free(za, sizeof(zap_attribute_t));
kmem_free(zc, sizeof(zap_cursor_t));
} }
static int static int