Merge PR #20469 into master

Merge PR #20469 into master

* refs/pull/20469/head:
	osd/PG: remove warn on delete+merge race
	osd: base project_pg_history on is_new_interval
	osd: make project_pg_history handle concurrent osdmap publish
	osd: handle pg delete vs merge race
	osd/PG: do not purge strays in premerge state
	doc/rados/operations/placement-groups: a few minor corrections
	doc/man/8/ceph: drop enumeration of pg states
	doc/dev/placement-groups: drop old 'splitting' reference
	osd: wait for laggy pgs without osd_lock in handle_osd_map
	osd: drain peering wq in start_boot, not _committed_maps
	osd: kick split children
	osd: no osd_lock for finish_splits
	osd/osd_types: remove is_split assert
	ceph-objectstore-tool: prevent import of pg that has since merged
	qa/suites: test pg merging
	qa/tasks/thrashosds: support merging pgs too
	mon/OSDMonitor: mon_inject_pg_merge_bounce_probability
	doc/rados/operations/placement-groups: update to describe pg_num reductions too
	doc/rados/operations: remove reference to lpgs
	osd: implement pg merge
	osd/PG: implement merge_from
	osdc/Objecter: resend ops on pg merge
	osd: collect and record pg_num changes by pool
	osd: make load_pgs remove message more accurate
	osd/osd_types: pg_t: add is_merge_target()
	osd/osd_types: pg_t::is_merge -> is_merge_source
	osd/osd_types: adding or substracting invalid stats -> invalid stats
	osd/PG: clear_ready_to_merge on_shutdown (or final merge source prep)
	osd: debug pending_creates_from_osd cleanup, don't use cbegin
	ceph-objectstore-tool: debug intervals update
	mgr/ClusterState: discard pg updates for pgs >= pg_num
	mon/OSDMonitor: fix long line
	mon/OSDMonitor: move pool created check into caller
	mon/OSDMonitor: adjust pgp_num_target down along with pg_num_target as needed
	mon/OSDMonitor: add mon_osd_max_initial_pgs to cap initial pool pgs
	osd/OSDMap: set pg[p]_num_target in build_simple*() methods
	mon/PGMap: adjust SMALLER_PGP_NUM warning to use *_target values
	mon/OSDMonitor: set CREATING flag for force-create-pg
	mon/OSDMonitor: start sending new-style pg_create2 messages
	mon/OSDMonitor: set last_force_resend_prenautilus for pg_num_pending changes
	osd: ignore pg creates when pool FLAG_CREATING is not set
	mgr: do not adjust pg_num until FLAG_CREATING removed from pool
	mon/OSDMonitor: add FLAG_CREATING on upgrade if pools still creating
	mon/OSDMonitor: prevent FLAG_CREATING from getting set pre-nautilus
	mon/OSDMonitor: disallow pg_num changes while CREATING flag is set
	mon/OSDMonitor: set POOL_CREATING flag until initial pool pgs are created
	osd/osd_types: add pg_pool_t FLAG_POOL_CREATING
	osd/osd_types: introduce last_force_resend_prenautilus
	osd/PGLog: merge_from helper
	osd: no cache agent or snap trimming during premerge
	osd: notify mon when pending PGs are ready to merge
	mgr: add simple controller to adjust pg[p]_num_actual
	mon/OSDMonitor: MOSDPGReadyToMerge to complete a pg_num change
	mon/OSDMonitor: allow pg_num to adjusted up or down via pg[p]_num_target
	osd/osd_types: make pg merge an interval boundary
	osd/osd_types: add pg_t::is_merge() method
	osd/osd_types: add pg_num_pending to pg_pool_t
	osd: allow multiple threads to block on wait_min_pg_epoch
	osd: restructure advance_pg() call mechanism
	mon/PGMap: prune merged pgs
	mon/PGMap: track pgs by state for each pool
	osd/SnapMapper: allow split_bits to decrease (merge)
	os/bluestore: fix osr_drain before merge
	os/bluestore: allow reuse of osr from existing collection
	os/filestore: (re)implement merge
	os/filestore: add _merge_collections post-check
	os: implement merge_collection
	os/ObjectStore: add merge_collection operation to Transaction