linux-kernel - Re: [PATCH] Supports to use the default CMA when the device-specified CMA memory is not enough.

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Message-ID: <2024061228-unburned-dander-c9a2@gregkh>
Date: Wed, 12 Jun 2024 09:20:02 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: "zhai.he" <zhai.he@....com>
Cc: akpm@...ux-foundation.org, sboyd@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	zhipeng.wang_1@....com, jindong.yue@....com
Subject: Re: [PATCH] Supports to use the default CMA when the
 device-specified CMA memory is not enough.

On Wed, Jun 12, 2024 at 10:38:31AM +0800, zhai.he wrote:
> From: He Zhai <zhai.he@....com>
> 
> In the current code logic, if the device-specified CMA memory
> allocation fails, memory will not be allocated from the default CMA area.
> This patch will use the default cma region when the device's
> specified CMA is not enough.
> 
> Signed-off-by: He Zhai <zhai.he@....com>
> ---
>  kernel/dma/contiguous.c | 11 +++++++++--
>  mm/cma.c                |  2 +-
>  2 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> index 055da410ac71..e45cfb24500f 100644
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -357,8 +357,13 @@ struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
>  	/* CMA can be used only in the context which permits sleeping */
>  	if (!gfpflags_allow_blocking(gfp))
>  		return NULL;
> -	if (dev->cma_area)
> -		return cma_alloc_aligned(dev->cma_area, size, gfp);
> +	if (dev->cma_area) {
> +		struct page *page = NULL;
> +
> +		page = cma_alloc_aligned(dev->cma_area, size, gfp);
> +		if (page)
> +			return page;
> +	}
>  	if (size <= PAGE_SIZE)
>  		return NULL;
>  
> @@ -406,6 +411,8 @@ void dma_free_contiguous(struct device *dev, struct page *page, size_t size)
>  	if (dev->cma_area) {
>  		if (cma_release(dev->cma_area, page, count))
>  			return;
> +		if (cma_release(dma_contiguous_default_area, page, count))
> +			return;
>  	} else {
>  		/*
>  		 * otherwise, page is from either per-numa cma or default cma
> diff --git a/mm/cma.c b/mm/cma.c
> index 3e9724716bad..f225b3f65bd2 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -495,7 +495,7 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
>  	}
>  
>  	if (ret && !no_warn) {
> -		pr_err_ratelimited("%s: %s: alloc failed, req-size: %lu pages, ret: %d\n",
> +		pr_debug("%s: %s: alloc failed, req-size: %lu pages, ret: %d, try to use default cma\n",
>  				   __func__, cma->name, count, ret);

Why did you change the error level here?

And when you use pr_debug(), you NEVER need to use __func__, as it is
already included automatically in the message output.  So now you have
it twice :)

thanks,

greg k-h