Re: [PATCH v3 2/5] dma-pool: allow user to disable atomic pool

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On 12/13/21 6:27 AM, Baoquan He wrote:
In the current code, three atomic memory pools are always created,
atomic_pool_kernel|dma|dma32, even though 'coherent_pool=0' is
specified in kernel command line. In fact, atomic pool is only
necessary when CONFIG_DMA_DIRECT_REMAP=y or mem_encrypt_active=y
which are needed on few ARCHes.

So change code to allow user to disable atomic pool by specifying
'coherent_pool=0'.

Meanwhile, update the relevant document in kernel-parameter.txt.

Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
>
 Acked-by: John Donnelly <john.p.donnelly@xxxxxxxxxx>
 Tested-by:  John Donnelly <john.p.donnelly@xxxxxxxxxx>

---
  Documentation/admin-guide/kernel-parameters.txt | 3 ++-
  kernel/dma/pool.c                               | 7 +++++--
  2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index ec4d25e854a8..d7015309614b 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -664,7 +664,8 @@
coherent_pool=nn[KMG] [ARM,KNL]
  			Sets the size of memory pool for coherent, atomic dma
-			allocations. Otherwise the default size will be scaled
+			allocations. A value of 0 disables the three atomic
+			memory pool. Otherwise the default size will be scaled
  			with memory capacity, while clamped between 128K and
  			1 << (PAGE_SHIFT + MAX_ORDER-1).
diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
index 5f84e6cdb78e..5a85804b5beb 100644
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -21,7 +21,7 @@ static struct gen_pool *atomic_pool_kernel __ro_after_init;
  static unsigned long pool_size_kernel;
/* Size can be defined by the coherent_pool command line */
-static size_t atomic_pool_size;
+static unsigned long atomic_pool_size = -1;
/* Dynamic background expansion when the atomic pool is near capacity */
  static struct work_struct atomic_pool_work;
@@ -188,11 +188,14 @@ static int __init dma_atomic_pool_init(void)
  {
  	int ret = 0;
+ if (!atomic_pool_size)
+		return 0;
+
  	/*
  	 * If coherent_pool was not used on the command line, default the pool
  	 * sizes to 128KB per 1GB of memory, min 128KB, max MAX_ORDER-1.
  	 */
-	if (!atomic_pool_size) {
+	if (atomic_pool_size == -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);





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