[PATCH v4 8/9] dmapool: improve accuracy of debug statistics

[PATCH v4 8/9] dmapool: improve accuracy of debug statistics

[Tony Battersby]

The "total number of blocks in pool" debug statistic currently does not
take the boundary value into account, so it diverges from the "total
number of blocks in use" statistic when a boundary is in effect.  Add a
calculation for the number of blocks per allocation that takes the
boundary into account, and use it to replace the inaccurate calculation.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
---

This depends on patch #1 "dmapool: fix boundary comparison" for the
calculated blks_per_alloc value to be correct.

The added blks_per_alloc value will also be used in the next patch.

--- linux/mm/dmapool.c.orig	2018-08-06 17:48:54.000000000 -0400
+++ linux/mm/dmapool.c	2018-08-06 17:52:53.000000000 -0400
@@ -61,6 +61,7 @@ struct dma_pool {		/* the pool */
 	struct device *dev;
 	unsigned int allocation;
 	unsigned int boundary;
+	unsigned int blks_per_alloc;
 	char name[32];
 	struct list_head pools;
 };
@@ -105,8 +106,7 @@ show_pools(struct device *dev, struct de
 		/* per-pool info, no real statistics yet */
 		temp = scnprintf(next, size, "%-16s %4zu %4zu %4u %2u\n",
 				 pool->name, blocks,
-				 (size_t) pages *
-				 (pool->allocation / pool->size),
+				 (size_t) pages * pool->blks_per_alloc,
 				 pool->size, pages);
 		size -= temp;
 		next += temp;
@@ -182,6 +182,9 @@ struct dma_pool *dma_pool_create(const c
 	retval->size = size;
 	retval->boundary = boundary;
 	retval->allocation = allocation;
+	retval->blks_per_alloc =
+		(allocation / boundary) * (boundary / size) +
+		(allocation % boundary) / size;
 
 	INIT_LIST_HEAD(&retval->pools);
 

Re: [PATCH v4 8/9] dmapool: improve accuracy of debug statistics

[Matthew Wilcox]

On Mon, Nov 12, 2018 at 10:45:58AM -0500, Tony Battersby wrote:
> +++ linux/mm/dmapool.c	2018-08-06 17:52:53.000000000 -0400
> @@ -61,6 +61,7 @@ struct dma_pool {		/* the pool */
>  	struct device *dev;
>  	unsigned int allocation;
>  	unsigned int boundary;
> +	unsigned int blks_per_alloc;
>  	char name[32];
>  	struct list_head pools;
>  };

This one I'm not totally happy with.  You're storing this value when
it could be easily calculated each time through the show_pools() code.
I appreciate this is a topic where reasonable people might have different
opinions about which solution is preferable.

> @@ -182,6 +182,9 @@ struct dma_pool *dma_pool_create(const c
>  	retval->size = size;
>  	retval->boundary = boundary;
>  	retval->allocation = allocation;
> +	retval->blks_per_alloc =
> +		(allocation / boundary) * (boundary / size) +
> +		(allocation % boundary) / size;
>  
>  	INIT_LIST_HEAD(&retval->pools);
>  
>