2022-07-03 11:51:35

by Feng Tang

Subject: [PATCH v2] iommu/iova: change IOVA_MAG_SIZE to 127 to save memory

kmalloc will round up the request size to power of 2, and current
iova_magazine's size is 1032 (1024+8) bytes, so each instance
allocated will get 2048 bytes from kmalloc, causing around 1KB
waste.

Change IOVA_MAG_SIZE from 128 to 127 to make size of 'iova_magazine'
1024 bytes so that no memory will be wasted.

Signed-off-by: Feng Tang <[email protected]>
Acked-by: Robin Murphy <[email protected]>
---
Changelog:

since v1:
* update commit log per the comments from Robin and John

drivers/iommu/iova.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index db77aa675145b..27634ddd9b904 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -614,7 +614,12 @@ EXPORT_SYMBOL_GPL(reserve_iova);
* dynamic size tuning described in the paper.
*/

-#define IOVA_MAG_SIZE 128
+/*
+ * As kmalloc's buffer size is fixed to power of 2, 127 is chosen to
+ * assure size of 'iova_magazine' to be 1024 bytes, so that no memory
+ * will be wasted.
+ */
+#define IOVA_MAG_SIZE 127
#define MAX_GLOBAL_MAGS 32 /* magazines per bin */

struct iova_magazine {
--
2.27.0

2022-07-06 11:42:45

by Joerg Roedel

Subject: Re: [PATCH v2] iommu/iova: change IOVA_MAG_SIZE to 127 to save memory

On Sun, Jul 03, 2022 at 07:44:50PM +0800, Feng Tang wrote:
> kmalloc will round up the request size to power of 2, and current
> iova_magazine's size is 1032 (1024+8) bytes, so each instance
> allocated will get 2048 bytes from kmalloc, causing around 1KB
> waste.
>
> Change IOVA_MAG_SIZE from 128 to 127 to make size of 'iova_magazine'
> 1024 bytes so that no memory will be wasted.
>
> Signed-off-by: Feng Tang <[email protected]>
> Acked-by: Robin Murphy <[email protected]>

Applied, thanks.