mm/swap: remove buggy cache->nr check in refill_swap_slots_cache

refill_swap_slots_cache is always called when cache->nr is 0.  So remove
such buggy and confusing check.

Link: https://lkml.kernel.org/r/20220509131416.17553-7-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Acked-by: NDavid Hildenbrand <david@redhat.com>
Reviewed-by: NOscar Salvador <osalvador@suse.de>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: NeilBrown <neilb@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>

mm/swap_slots.c

@@ -258,7 +258,7 @@ void enable_swap_slots_cache(void)
 /* called with swap slot cache's alloc lock held */
 static int refill_swap_slots_cache(struct swap_slots_cache *cache)
 {
-	if (!use_swap_slot_cache || cache->nr)
+	if (!use_swap_slot_cache)
 		return 0;
 
 	cache->cur = 0;