From b5edb374605c02a670d8c627bc9b5bb2b66ca340 Mon Sep 17 00:00:00 2001
From: Sage Weil <sage@newdream.net>
Date: Tue, 30 Nov 2021 18:18:31 -0500
Subject: [PATCH] mgr: limit changes to pg_num

We need to avoid making drastic changes to pg_num that outpace pgp_num or
else we will may hit the per-osd pg limits.

Fixes: https://tracker.ceph.com/issues/53442
Signed-off-by: Sage Weil <sage@newdream.net>
(cherry picked from commit 3b2a11249aff6ee608efc95212d6723df180cd07)

 Conflicts:
	src/common/options/mgr.yaml.in - old way of specifying config settings
---
 src/common/legacy_config_opts.h |  2 ++
 src/common/options.cc           |  5 +++++
 src/mgr/DaemonServer.cc         | 11 ++++++++++-
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/common/legacy_config_opts.h b/src/common/legacy_config_opts.h
index d22061f8a7d53..c06d2f15304f1 100644
--- a/src/common/legacy_config_opts.h
+++ b/src/common/legacy_config_opts.h
@@ -305,6 +305,8 @@ OPTION(mon_debug_unsafe_allow_tier_with_nonempty_snaps, OPT_BOOL)
 OPTION(mon_osd_blocklist_default_expire, OPT_DOUBLE) // default one hour
 OPTION(mon_osd_crush_smoke_test, OPT_BOOL)
 
+OPTION(mgr_max_pg_num_change, OPT_INT)
+
 OPTION(paxos_stash_full_interval, OPT_INT)   // how often (in commits) to stash a full copy of the PaxosService state
 OPTION(paxos_max_join_drift, OPT_INT) // max paxos iterations before we must first sync the monitor stores
 OPTION(paxos_propose_interval, OPT_DOUBLE)  // gather updates for this long before proposing a map update
diff --git a/src/common/options.cc b/src/common/options.cc
index 89f3418f66d81..86535c128a48a 100644
--- a/src/common/options.cc
+++ b/src/common/options.cc
@@ -5482,6 +5482,11 @@ std::vector<Option> get_global_options() {
     .add_service("mgr")
     .set_description("Path to cephadm utility"),
 
+    Option("mgr_max_pg_num_change", Option::TYPE_INT, Option::LEVEL_ADVANCED)
+    .set_default(128)
+    .add_service("mgr")
+    .set_description("maximum change in pg_num"),
+
     Option("mgr_module_path", Option::TYPE_STR, Option::LEVEL_ADVANCED)
     .set_default(CEPH_DATADIR "/mgr")
     .add_service("mgr")
diff --git a/src/mgr/DaemonServer.cc b/src/mgr/DaemonServer.cc
index 48534f896ac49..f95277f2958a1 100644
--- a/src/mgr/DaemonServer.cc
+++ b/src/mgr/DaemonServer.cc
@@ -2765,15 +2765,24 @@ void DaemonServer::adjust_pgs()
 	    } else {
 	      active = false;
 	    }
+	    unsigned pg_gap = p.get_pg_num() - p.get_pgp_num();
+	    unsigned max_jump = cct->_conf->mgr_max_pg_num_change;
 	    if (!active) {
 	      dout(10) << "pool " << i.first
 		       << " pg_num_target " << p.get_pg_num_target()
 		       << " pg_num " << p.get_pg_num()
 		       << " - not all pgs active"
 		       << dendl;
+	    } else if (pg_gap >= max_jump) {
+	      dout(10) << "pool " << i.first
+		       << " pg_num " << p.get_pg_num()
+		       << " - pgp_num " << p.get_pgp_num()
+		       << " gap > max_pg_num_change " << max_jump
+		       << " - must scale pgp_num first"
+		       << dendl;
 	    } else {
 	      unsigned add = std::min(
-		left,
+		std::min(left, max_jump - pg_gap),
 		p.get_pg_num_target() - p.get_pg_num());
 	      unsigned target = p.get_pg_num() + add;
 	      left -= add;
-- 
2.39.5