swiotlb: check alloc_size before the allocation of a new memory pool

The allocation request for swiotlb contiguous memory greater than
128*2KB cannot be fulfilled because it exceeds the maximum contiguous
memory limit. If the swiotlb memory we allocate is larger than 128*2KB,
swiotlb_find_slots() will still schedule the allocation of a new memory
pool, which will increase memory overhead.

Fix it by adding a check with alloc_size no more than 128*2KB before
scheduling the allocation of a new memory pool in swiotlb_find_slots().

Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Petr Tesarik <petr.tesarik1@huawei-partners.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Author: ZhangPeng

kernel/dma/swiotlb.c

@@ -1136,6 +1136,9 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
 	int cpu, i;
 	int index;
 
+	if (alloc_size > IO_TLB_SEGSIZE * IO_TLB_SIZE)
+		return -1;
+
 	cpu = raw_smp_processor_id();
 	for (i = 0; i < default_nareas; ++i) {
 		index = swiotlb_search_area(dev, cpu, i, orig_addr, alloc_size,