dma-pool: fix too large DMA pools on medium memory size systems

On systems with at least 32 MiB, but less than 32 GiB of RAM, the DMA
memory pools are much larger than intended (e.g. 2 MiB instead of 128
KiB on a 256 MiB system).

Fix this by correcting the calculation of the number of GiBs of RAM in
the system.  Invert the order of the min/max operations, to keep on
calculating in pages until the last step, which aids readability.

Fixes: 1d659236 ("dma-pool: scale the default DMA coherent pool size with memory capacity")
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Acked-by: NDavid Rientjes <rientjes@google.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

kernel/dma/pool.c

@@ -175,10 +175,9 @@ static int __init dma_atomic_pool_init(void)
 	 * sizes to 128KB per 1GB of memory, min 128KB, max MAX_ORDER-1.
 	 */
 	if (!atomic_pool_size) {
-		atomic_pool_size = max(totalram_pages() >> PAGE_SHIFT, 1UL) *
-					SZ_128K;
-		atomic_pool_size = min_t(size_t, atomic_pool_size,
-					 1 << (PAGE_SHIFT + MAX_ORDER-1));
+		unsigned long pages = totalram_pages() / (SZ_1G / SZ_128K);
+		pages = min_t(unsigned long, pages, MAX_ORDER_NR_PAGES);
+		atomic_pool_size = max_t(size_t, pages << PAGE_SHIFT, SZ_128K);
 	}
 	INIT_WORK(&atomic_pool_work, atomic_pool_work_fn);