[PATCH v2] dma-pool: Fix too large DMA pools on medium systems

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Christoph Hellwig <hch@lst.de>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>,
	David Rientjes <rientjes@google.com>
Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
	Geert Uytterhoeven <geert@linux-m68k.org>
Subject: [PATCH v2] dma-pool: Fix too large DMA pools on medium systems
Date: Mon,  8 Jun 2020 15:22:17 +0200	[thread overview]
Message-ID: <20200608132217.29945-1-geert@linux-m68k.org> (raw)

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: 1d659236fb43c4d2 ("dma-pool: scale the default DMA coherent pool size with memory capacity")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
v2:
  - Improve readability:
      - Divide by (SZ_1G / SZ_128K) instead of using a shift,
      - Invert min/max order to keep calculating in pages until the last
	step.
---
 kernel/dma/pool.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
index 35bb51c31fff370f..8cfa01243ed27b6f 100644
--- a/kernel/dma/pool.c
+++ b/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);
 
-- 
2.17.1

