Re: [RFC 3/3] mm: integrate GCMA with CMA using dt-bindings

[Conor Dooley <conor@kernel.org>]

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On Thu, Mar 20, 2025 at 10:39:31AM -0700, Suren Baghdasaryan wrote:
> This patch introduces a new "guarantee" property for shared-dma-pool.
> With this property, admin can create specific memory pool as
> GCMA-based CMA if they care about allocation success rate and latency.
> The downside of GCMA is that it can host only clean file-backed pages
> since it's using cleancache as its secondary user.
> 
> Signed-off-by: Minchan Kim <minchan@google.com>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
>  arch/powerpc/kernel/fadump.c |  2 +-
>  include/linux/cma.h          |  2 +-
>  kernel/dma/contiguous.c      | 11 ++++++++++-
>  mm/cma.c                     | 33 ++++++++++++++++++++++++++-------
>  mm/cma.h                     |  1 +
>  mm/cma_sysfs.c               | 10 ++++++++++
>  6 files changed, 49 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
> index 4b371c738213..4eb7be0cdcdb 100644
> --- a/arch/powerpc/kernel/fadump.c
> +++ b/arch/powerpc/kernel/fadump.c
> @@ -111,7 +111,7 @@ void __init fadump_cma_init(void)
>  		return;
>  	}
>  
> -	rc = cma_init_reserved_mem(base, size, 0, "fadump_cma", &fadump_cma);
> +	rc = cma_init_reserved_mem(base, size, 0, "fadump_cma", &fadump_cma, false);
>  	if (rc) {
>  		pr_err("Failed to init cma area for firmware-assisted dump,%d\n", rc);
>  		/*
> diff --git a/include/linux/cma.h b/include/linux/cma.h
> index 62d9c1cf6326..3207db979e94 100644
> --- a/include/linux/cma.h
> +++ b/include/linux/cma.h
> @@ -46,7 +46,7 @@ extern int __init cma_declare_contiguous_multi(phys_addr_t size,
>  extern int cma_init_reserved_mem(phys_addr_t base, phys_addr_t size,
>  					unsigned int order_per_bit,
>  					const char *name,
> -					struct cma **res_cma);
> +					struct cma **res_cma, bool gcma);
>  extern struct page *cma_alloc(struct cma *cma, unsigned long count, unsigned int align,
>  			      bool no_warn);
>  extern bool cma_pages_valid(struct cma *cma, const struct page *pages, unsigned long count);
> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> index 055da410ac71..a68b3123438c 100644
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -459,6 +459,7 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
>  	unsigned long node = rmem->fdt_node;
>  	bool default_cma = of_get_flat_dt_prop(node, "linux,cma-default", NULL);
>  	struct cma *cma;
> +	bool gcma;
>  	int err;
>  
>  	if (size_cmdline != -1 && default_cma) {
> @@ -476,7 +477,15 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
>  		return -EINVAL;
>  	}
>  
> -	err = cma_init_reserved_mem(rmem->base, rmem->size, 0, rmem->name, &cma);
> +	gcma = !!of_get_flat_dt_prop(node, "guarantee", NULL);

When this (or if I guess) this goes !RFC, you will need to document this
new property that you're adding.

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