[PATCH] fix creating zero sized bio mempools in low memory system

In the very low memory systems is in the init_bio call
scale parameter set to zero and it leads to creating
zero sized mempool.

This patch prevents pool_entries parameter become zero,
so the created pool have at least 1 entry.

Mempool with 0 entries lead to incorrect behaviour
of mempool_free. (Alloc requests are not waken up
and system stalls in mempool_alloc->ioschedule).
Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/bio.c

@@ -1142,7 +1142,7 @@ static int biovec_create_pools(struct bio_set *bs, int pool_entries, int scale)
 		struct biovec_slab *bp = bvec_slabs + i;
 		mempool_t **bvp = bs->bvec_pools + i;
 
-		if (i >= scale)
+		if (pool_entries > 1 && i >= scale)
 			pool_entries >>= 1;
 
 		*bvp = mempool_create_slab_pool(pool_entries, bp->slab);