revert: remove access-frequency ILM tiering (#60)

Reverse the first-parent diff of a3df317ae0,
including the feature branch compatibility and mover follow-up fixes.
Retain the independent multi-pool correctness fixes from #178 and migrate
their shared test fixture away from access-tier code.

Tolerate retired ILM keys and XML, read old v9 statistics while writing v8,
and document migration without moving objects or rewriting their metadata.
Include regression coverage using a historical scanner/writer v9 fixture.

Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/ilm-config.go

@@ -19,7 +19,6 @@ package cmd
 
 import (
 	"sync"
-	"time"
 
 	"github.com/minio/minio/internal/config/ilm"
 )
@@ -28,16 +27,6 @@ var globalILMConfig = ilmConfig{
 	cfg: ilm.Config{
 		ExpirationWorkers: 100,
 		TransitionWorkers: 100,
-		// Access tiering stays off until configured, but the counter
-		// geometry must be sane from the start: the tracker divides by
-		// AccessBinWidth before any config is loaded.
-		AccessPromoteWatermark: 85,
-		AccessBinWidth:         time.Minute,
-		AccessBins:             12,
-		AccessFlush:            time.Minute,
-		AccessMinResidency:     24 * time.Hour,
-		AccessWorkers:          10,
-		AccessMaxTracked:       1000000,
 	},
 }
 
@@ -60,25 +49,6 @@ func (c *ilmConfig) getTransitionWorkers() int {
 	return c.cfg.TransitionWorkers
 }
 
-// accessCfg returns a copy of the access tiering settings. Callers take the
-// whole struct rather than one getter per field because the promotion and
-// demotion paths need a consistent view of several knobs at once.
-func (c *ilmConfig) accessCfg() ilm.Config {
-	c.mu.RLock()
-	defer c.mu.RUnlock()
-
-	return c.cfg
-}
-
-// accessTieringEnabled is the cheap gate used on the scanner path.
-func (c *ilmConfig) accessTieringEnabled() bool {
-	c.mu.RLock()
-	defer c.mu.RUnlock()
-
-	_, ok := c.cfg.HotPool()
-	return ok
-}
-
 func (c *ilmConfig) update(cfg ilm.Config) {
 	c.mu.Lock()
 	defer c.mu.Unlock()