bcache: bugfix - moving_gc now moves only correct buckets

Removed gc_move_threshold because picking buckets only by
threshold could lead moving extra buckets (ei. if there are
buckets at the threshold that aren't supposed to be moved
do to space considerations).

This is replaced by a GC_MOVE bit in the gc_mark bitmask.
Now only marked buckets get moved.

Signed-off-by: Nicholas Swenson <nks@daterainc.com>
Signed-off-by: Kent Overstreet <kmo@daterainc.com>

drivers/md/bcache/alloc.c

@@ -421,9 +421,11 @@ long bch_bucket_alloc(struct cache *ca, unsigned watermark, bool wait)
 
 	if (watermark <= WATERMARK_METADATA) {
 		SET_GC_MARK(b, GC_MARK_METADATA);
+		SET_GC_MOVE(b, 0);
 		b->prio = BTREE_PRIO;
 	} else {
 		SET_GC_MARK(b, GC_MARK_RECLAIMABLE);
+		SET_GC_MOVE(b, 0);
 		b->prio = INITIAL_PRIO;
 	}
 

drivers/md/bcache/bcache.h

@@ -197,7 +197,7 @@ struct bucket {
 	uint8_t		disk_gen;
 	uint8_t		last_gc; /* Most out of date gen in the btree */
 	uint8_t		gc_gen;
-	uint16_t	gc_mark;
+	uint16_t	gc_mark; /* Bitfield used by GC. See below for field */
 };
 
 /*
@@ -209,7 +209,8 @@ BITMASK(GC_MARK,	 struct bucket, gc_mark, 0, 2);
 #define GC_MARK_RECLAIMABLE	0
 #define GC_MARK_DIRTY		1
 #define GC_MARK_METADATA	2
-BITMASK(GC_SECTORS_USED, struct bucket, gc_mark, 2, 14);
+BITMASK(GC_SECTORS_USED, struct bucket, gc_mark, 2, 13);
+BITMASK(GC_MOVE, struct bucket, gc_mark, 15, 1);
 
 #include "journal.h"
 #include "stats.h"
@@ -445,7 +446,6 @@ struct cache {
 	 * call prio_write() to keep gens from wrapping.
 	 */
 	uint8_t			need_save_prio;
-	unsigned		gc_move_threshold;
 
 	/*
 	 * If nonzero, we know we aren't going to find any buckets to invalidate

drivers/md/bcache/movinggc.c

@@ -25,10 +25,9 @@ static bool moving_pred(struct keybuf *buf, struct bkey *k)
 	unsigned i;
 
 	for (i = 0; i < KEY_PTRS(k); i++) {
-		struct cache *ca = PTR_CACHE(c, k, i);
 		struct bucket *g = PTR_BUCKET(c, k, i);
 
-		if (GC_SECTORS_USED(g) < ca->gc_move_threshold)
+		if (GC_MOVE(g))
 			return true;
 	}
 
@@ -227,9 +226,8 @@ void bch_moving_gc(struct cache_set *c)
 			sectors_to_move -= GC_SECTORS_USED(b);
 		}
 
-		ca->gc_move_threshold = bucket_heap_top(ca);
-
-		pr_debug("threshold %u", ca->gc_move_threshold);
+		while (heap_pop(&ca->heap, b, bucket_cmp))
+			SET_GC_MOVE(b, 1);
 	}
 
 	mutex_unlock(&c->bucket_lock);