linux-kernel - [PATCH v6 05/11] dmapool: improve accuracy of debug statistics

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Date:   Tue, 7 Jun 2022 14:42:56 -0400
From:   Tony Battersby <tonyb@...ernetics.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     iommu@...ts.linux-foundation.org, kernel-team@...com,
        Matthew Wilcox <willy@...radead.org>,
        Keith Busch <kbusch@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Tony Lindgren <tony@...mide.com>
Subject: [PATCH v6 05/11] dmapool: improve accuracy of debug statistics

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.

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

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

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

 mm/dmapool.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/dmapool.c b/mm/dmapool.c
index 122781fe2c03..d3e5a6151fb4 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -47,6 +47,7 @@ struct dma_pool {		/* the pool */
 	unsigned int size;
 	unsigned int allocation;
 	unsigned int boundary;
+	unsigned int blks_per_alloc;
 	char name[32];
 	struct list_head pools;
 };
@@ -85,8 +86,7 @@ static ssize_t pools_show(struct device *dev, struct device_attribute *attr, cha
 		/* per-pool info, no real statistics yet */
 		size += sysfs_emit_at(buf, 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);
 	}
 	mutex_unlock(&pools_lock);
@@ -159,6 +159,9 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
 	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);
 
-- 
2.25.1