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

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Date:   Mon, 13 Dec 2021 08:21:29 -0600
From:   john.p.donnelly@...cle.com
To:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org, hch@....de,
        cl@...ux.com, John.p.donnelly@...cle.com, kexec@...ts.infradead.org
Subject: Re: [PATCH v3 2/5] dma-pool: allow user to disable atomic pool

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@...hat.com>
 >
  Acked-by: John Donnelly <john.p.donnelly@...cle.com>
  Tested-by:  John Donnelly <john.p.donnelly@...cle.com>

> ---
>   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);