Re: [PATCH RESEND v2 2/5] dma-pool: allow user to disable atomic pool

John Donnelly
2021-12-07T03:54:48Z

On 12/6/21 9:07 PM, 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@redhat.com>

Reviewed-by: John Donnelly <john.p.donnelly@oracle.com>
Tested-by: John Donnelly <john.p.donnelly@oracle.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);
>