linux-kernel - [PATCH v2] mm/dmapool.c: avoid duplicate memset within dma_pool

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Date:   Mon, 18 Jul 2022 14:28:10 +0800
From:   Liu Song <liusong@...ux.alibaba.com>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] mm/dmapool.c: avoid duplicate memset within dma_pool_alloc

From: Liu Song <liusong@...ux.alibaba.com>

In "dma_alloc_from_dev_coherent" and "dma_direct_alloc",
the allocated memory is explicitly set to 0.

A helper function "use_dev_coherent_memory" is introduced here to
determine whether the memory is allocated by "dma_alloc_from_dev_coherent".

And use "get_dma_ops" to determine whether the memory is allocated by
"dma_direct_alloc".

After this modification, memory allocated using "dma_pool_zalloc" can avoid
duplicate memset.

Signed-off-by: Liu Song <liusong@...ux.alibaba.com>
---
 include/linux/dma-map-ops.h | 5 +++++
 mm/dmapool.c                | 5 ++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index 0d5b06b..c29948d 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -171,6 +171,10 @@ int dma_alloc_from_dev_coherent(struct device *dev, ssize_t size,
 int dma_release_from_dev_coherent(struct device *dev, int order, void *vaddr);
 int dma_mmap_from_dev_coherent(struct device *dev, struct vm_area_struct *vma,
 		void *cpu_addr, size_t size, int *ret);
+static inline bool use_dev_coherent_memory(struct device *dev)
+{
+	return dev->dma_mem ? true : false;
+}
 #else
 static inline int dma_declare_coherent_memory(struct device *dev,
 		phys_addr_t phys_addr, dma_addr_t device_addr, size_t size)
@@ -180,6 +184,7 @@ static inline int dma_declare_coherent_memory(struct device *dev,
 #define dma_alloc_from_dev_coherent(dev, size, handle, ret) (0)
 #define dma_release_from_dev_coherent(dev, order, vaddr) (0)
 #define dma_mmap_from_dev_coherent(dev, vma, vaddr, order, ret) (0)
+#define use_dev_coherent_memory(dev) (0)
 #endif /* CONFIG_DMA_DECLARE_COHERENT */
 
 #ifdef CONFIG_DMA_GLOBAL_POOL
diff --git a/mm/dmapool.c b/mm/dmapool.c
index a7eb5d0..6e03530 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -21,6 +21,7 @@
 
 #include <linux/device.h>
 #include <linux/dma-mapping.h>
+#include <linux/dma-map-ops.h>
 #include <linux/dmapool.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
@@ -372,7 +373,9 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
 #endif
 	spin_unlock_irqrestore(&pool->lock, flags);
 
-	if (want_init_on_alloc(mem_flags))
+	if (want_init_on_alloc(mem_flags) &&
+		!use_dev_coherent_memory(pool->dev) &&
+		get_dma_ops(pool->dev))
 		memset(retval, 0, pool->size);
 
 	return retval;
-- 
1.8.3.1