bcache: Kill bucket->gc_gen

gc_gen was a temporary used to recalculate last_gc, but since we only need
bucket->last_gc when gc isn't running (gc_mark_valid = 1), we can just update
last_gc directly.

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

drivers/md/bcache/bcache.h

@@ -196,7 +196,6 @@ struct bucket {
 	uint16_t	prio;
 	uint8_t		gen;
 	uint8_t		last_gc; /* Most out of date gen in the btree */
-	uint8_t		gc_gen;
 	uint16_t	gc_mark; /* Bitfield used by GC. See below for field */
 };
 
@@ -588,7 +587,7 @@ struct cache_set {
 	uint16_t		min_prio;
 
 	/*
-	 * max(gen - gc_gen) for all buckets. When it gets too big we have to gc
+	 * max(gen - last_gc) for all buckets. When it gets too big we have to gc
 	 * to keep gens from wrapping around.
 	 */
 	uint8_t			need_gc;

drivers/md/bcache/btree.c

@@ -1178,8 +1178,8 @@ static uint8_t __bch_btree_mark_key(struct cache_set *c, int level,
 
 		g = PTR_BUCKET(c, k, i);
 
-		if (gen_after(g->gc_gen, PTR_GEN(k, i)))
-			g->gc_gen = PTR_GEN(k, i);
+		if (gen_after(g->last_gc, PTR_GEN(k, i)))
+			g->last_gc = PTR_GEN(k, i);
 
 		if (ptr_stale(c, k, i)) {
 			stale = max(stale, ptr_stale(c, k, i));
@@ -1631,7 +1631,7 @@ static void btree_gc_start(struct cache_set *c)
 
 	for_each_cache(ca, c, i)
 		for_each_bucket(b, ca) {
-			b->gc_gen = b->gen;
+			b->last_gc = b->gen;
 			if (!atomic_read(&b->pin)) {
 				SET_GC_MARK(b, 0);
 				SET_GC_SECTORS_USED(b, 0);
@@ -1693,7 +1693,6 @@ static size_t bch_btree_gc_finish(struct cache_set *c)
 			SET_GC_MARK(ca->buckets + *i, GC_MARK_METADATA);
 
 		for_each_bucket(b, ca) {
-			b->last_gc	= b->gc_gen;
 			c->need_gc	= max(c->need_gc, bucket_gc_gen(b));
 
 			if (atomic_read(&b->pin))

drivers/md/bcache/extents.c

@@ -194,9 +194,9 @@ err:
 	mutex_unlock(&b->c->bucket_lock);
 	bch_extent_to_text(buf, sizeof(buf), k);
 	btree_bug(b,
-"inconsistent btree pointer %s: bucket %zi pin %i prio %i gen %i last_gc %i mark %llu gc_gen %i",
+"inconsistent btree pointer %s: bucket %zi pin %i prio %i gen %i last_gc %i mark %llu",
 		  buf, PTR_BUCKET_NR(b->c, k, i), atomic_read(&g->pin),
-		  g->prio, g->gen, g->last_gc, GC_MARK(g), g->gc_gen);
+		  g->prio, g->gen, g->last_gc, GC_MARK(g));
 	return true;
 }
 
@@ -515,9 +515,9 @@ err:
 	mutex_unlock(&b->c->bucket_lock);
 	bch_extent_to_text(buf, sizeof(buf), k);
 	btree_bug(b,
-"inconsistent extent pointer %s:\nbucket %zu pin %i prio %i gen %i last_gc %i mark %llu gc_gen %i",
+"inconsistent extent pointer %s:\nbucket %zu pin %i prio %i gen %i last_gc %i mark %llu",
 		  buf, PTR_BUCKET_NR(b->c, k, ptr), atomic_read(&g->pin),
-		  g->prio, g->gen, g->last_gc, GC_MARK(g), g->gc_gen);
+		  g->prio, g->gen, g->last_gc, GC_MARK(g));
 	return true;
 }
 

drivers/md/bcache/super.c

@@ -635,7 +635,7 @@ static void prio_read(struct cache *ca, uint64_t bucket)
 		}
 
 		b->prio = le16_to_cpu(d->prio);
-		b->gen = b->last_gc = b->gc_gen = d->gen;
+		b->gen = b->last_gc = d->gen;
 	}
 }