linux-kernel - Re: [PATCH v2] cma: introduce CMA_ALLOC

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Date:   Wed, 9 Aug 2023 19:27:52 +0530
From:   Bibek Kumar Patro <quic_bibekkum@...cinc.com>
To:     <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <quic_pkondeti@...cinc.com>, <quic_charante@...cinc.com>
Subject: Re: [PATCH v2] cma: introduce CMA_ALLOC_DEBUG config

v2 was added by mistake. It's first submission of the patch. Please 
ignore the v2.

regards,
Bibek

On 8/9/2023 6:46 PM, Bibek Kumar Patro wrote:
> Currently enabling CONFIG_CMA_DEBUG enables DEBUG preprocessor macro.
> If DEBUG is defined, it's equivalent to a printk with KERN_DEBUG loglevel
> flooding the dmesg buffer with pr_debug prints from mm/cma driver and from
> included files as well. This results in excessive amount of CMA logging and
> also might distract the debug teams with unrelated KERN_DEBUG prints.One of
> the ways engineers currently tackle this problem is by passing loglevel=N
> though commandline to suppress KERN_DEBUG messages. This approach can
> sometimes become tiresome due to its repetitive nature.
> This patch proposes an alternative approach by introducing a simple new
> config CONFIG_CMA_ALLOC_DEBUG which only shows the cma bit allocation
> status in case of cma failure and do not enable DEBUG preprocessor macro
> from CONFIG_CMA_DEBUG avoiding excessive CMA logging from pr_debug.
> Engineers and tech teams seeking only for bitmap status in case of cma
> failure can use this simple config instead of worrying about changing
> the loglevel or trying other similar workarounds.
> 
> Signed-off-by: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
> ---
>   mm/Kconfig | 11 +++++++++++
>   mm/cma.c   |  2 +-
>   2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 09130434e30d..ad2a20576a65 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -891,12 +891,23 @@ config CMA
>   config CMA_DEBUG
>   	bool "CMA debug messages (DEVELOPMENT)"
>   	depends on DEBUG_KERNEL && CMA
> +	select CMA_ALLOC_DEBUG
>   	help
>   	  Turns on debug messages in CMA.  This produces KERN_DEBUG
>   	  messages for every CMA call as well as various messages while
>   	  processing calls such as dma_alloc_from_contiguous().
>   	  This option does not affect warning and error messages.
> 
> +config CMA_ALLOC_DEBUG
> +	bool "CMA bitmap status upon failure"
> +	depends on CMA
> +	help
> +	  Turns on bitmap dump in case of cma failures. This prints
> +	  current status of CMA bit upon failures and will appear
> +	  when cma_alloc() return no_warn argument as false and won't
> +	  flood the dmesg buffer with unrelated KERN_DEBUG prints. No
> +	  need to explicitly enable this if CMA_DEBUG is enabled.
> +
>   config CMA_DEBUGFS
>   	bool "CMA debugfs interface"
>   	depends on CMA && DEBUG_FS
> diff --git a/mm/cma.c b/mm/cma.c
> index a4cfe995e11e..0ead392769b3 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -383,7 +383,7 @@ int __init cma_declare_contiguous_nid(phys_addr_t base,
>   	return ret;
>   }
> 
> -#ifdef CONFIG_CMA_DEBUG
> +#ifdef CONFIG_CMA_ALLOC_DEBUG
>   static void cma_debug_show_areas(struct cma *cma)
>   {
>   	unsigned long next_zero_bit, next_set_bit, nr_zero;
> --
> 2.17.1
>