From 5815f7ac30e108fcbf4c6487328c28d818e9e014 Mon Sep 17 00:00:00 2001 From: Tom Caputi Date: Wed, 11 Sep 2019 14:16:48 -0400 Subject: [PATCH] Fix stalled txg with repeated noop scans Currently, the DSL scan code figures out when it should suspend processing and allow a txg to continue by calling the function dsl_scan_check_suspend(). Unfortunately, this function only allows the scan to suspend at a level 0 block. In the event that the system is scanning a bunch of empty snapshots or a resilver is running with a high enough scn_cur_min_txg, the scan will stop processing each dataset at the root level, deciding it has nothing left to do. This means that the check_suspend function is never called and the txg remains stuck until a dataset is found that has data to scan. This patch fixes the problem by allowing scans to suspend at the root level of the objset. For backwards compatibility, we use the bookmark when we suspend here so that older versions of the code will work as intended. Reviewed-by: Matt Ahrens Reviewed-by: Brian Behlendorf Signed-off-by: Tom Caputi Closes #9300 --- module/zfs/dsl_scan.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/module/zfs/dsl_scan.c b/module/zfs/dsl_scan.c index 160bc8ff3..ec71a6d91 100644 --- a/module/zfs/dsl_scan.c +++ b/module/zfs/dsl_scan.c @@ -1272,8 +1272,8 @@ dsl_scan_check_suspend(dsl_scan_t *scn, const zbookmark_phys_t *zb) if (!ZB_IS_ZERO(&scn->scn_phys.scn_bookmark)) return (B_FALSE); /* we're resuming */ - /* We only know how to resume from level-0 blocks. */ - if (zb && zb->zb_level != 0) + /* We only know how to resume from level-0 and objset blocks. */ + if (zb && (zb->zb_level != 0 && zb->zb_level != ZB_ROOT_LEVEL)) return (B_FALSE); /* @@ -1304,7 +1304,16 @@ dsl_scan_check_suspend(dsl_scan_t *scn, const zbookmark_phys_t *zb) NSEC2SEC(sync_time_ns) >= zfs_txg_timeout)) || spa_shutting_down(scn->scn_dp->dp_spa) || (zfs_scan_strict_mem_lim && dsl_scan_should_clear(scn))) { - if (zb) { + if (zb && zb->zb_level == ZB_ROOT_LEVEL) { + dprintf("suspending at first available bookmark " + "%llx/%llx/%llx/%llx\n", + (longlong_t)zb->zb_objset, + (longlong_t)zb->zb_object, + (longlong_t)zb->zb_level, + (longlong_t)zb->zb_blkid); + SET_BOOKMARK(&scn->scn_phys.scn_bookmark, + zb->zb_objset, 0, 0, 0); + } else if (zb != NULL) { dprintf("suspending at bookmark %llx/%llx/%llx/%llx\n", (longlong_t)zb->zb_objset, (longlong_t)zb->zb_object,