bcache: Use a mempool for mergesort temporary space

It was a single element mempool before, it's slightly cleaner to just use a real
mempool.
Signed-off-by: Kent Overstreet <kmo@daterainc.com>

drivers/md/bcache/bcache.h

@@ -645,12 +645,7 @@ struct cache_set {
 	 */
 	mempool_t		*fill_iter;
 
-	/*
-	 * btree_sort() is a merge sort and requires temporary space - single
-	 * element mempool
-	 */
-	struct mutex		sort_lock;
-	struct bset		*sort;
+	mempool_t		*sort_pool;
 	unsigned		sort_crit_factor;
 
 	/* List of buckets we're currently writing data to */

drivers/md/bcache/bset.c

@@ -1047,11 +1047,12 @@ static void __btree_sort(struct btree *b, struct btree_iter *iter,
 {
 	uint64_t start_time;
 	bool remove_stale = !b->written;
+	bool used_mempool = false;
 	struct bset *out = (void *) __get_free_pages(__GFP_NOWARN|GFP_NOIO,
 						     order);
 	if (!out) {
-		mutex_lock(&b->c->sort_lock);
-		out = b->c->sort;
+		out = page_address(mempool_alloc(b->c->sort_pool, GFP_NOIO));
+		used_mempool = true;
 		order = ilog2(bucket_pages(b->c));
 	}
 
@@ -1071,17 +1072,14 @@ static void __btree_sort(struct btree *b, struct btree_iter *iter,
 		out->seq	= b->sets[0].data->seq;
 		out->version	= b->sets[0].data->version;
 		swap(out, b->sets[0].data);
-
-		if (b->c->sort == b->sets[0].data)
-			b->c->sort = out;
 	} else {
 		b->sets[start].data->keys = out->keys;
 		memcpy(b->sets[start].data->start, out->start,
 		       (void *) end(out) - (void *) out->start);
 	}
 
-	if (out == b->c->sort)
-		mutex_unlock(&b->c->sort_lock);
+	if (used_mempool)
+		mempool_free(virt_to_page(out), b->c->sort_pool);
 	else
 		free_pages((unsigned long) out, order);
 

drivers/md/bcache/super.c

@@ -1352,7 +1352,6 @@ static void cache_set_free(struct closure *cl)
 			kobject_put(&ca->kobj);
 
 	free_pages((unsigned long) c->uuids, ilog2(bucket_pages(c)));
-	free_pages((unsigned long) c->sort, ilog2(bucket_pages(c)));
 
 	if (c->bio_split)
 		bioset_free(c->bio_split);
@@ -1489,7 +1488,6 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
 	init_waitqueue_head(&c->try_wait);
 	init_waitqueue_head(&c->bucket_wait);
 	sema_init(&c->uuid_write_mutex, 1);
-	mutex_init(&c->sort_lock);
 
 	spin_lock_init(&c->sort_time.lock);
 	spin_lock_init(&c->btree_gc_time.lock);
@@ -1519,7 +1517,8 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
 				bucket_pages(c))) ||
 	    !(c->fill_iter = mempool_create_kmalloc_pool(1, iter_size)) ||
 	    !(c->bio_split = bioset_create(4, offsetof(struct bbio, bio))) ||
-	    !(c->sort = alloc_bucket_pages(GFP_KERNEL, c)) ||
+	    !(c->sort_pool = mempool_create_page_pool(1,
+				ilog2(bucket_pages(c)))) ||
 	    !(c->uuids = alloc_bucket_pages(GFP_KERNEL, c)) ||
 	    bch_journal_alloc(c) ||
 	    bch_btree_cache_alloc(c) ||