linux-kernel - Re: [PATCH v4] mm: cma: support sysfs

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Date:   Fri, 5 Mar 2021 18:34:22 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        gregkh@...uxfoundation.org, surenb@...gle.com, joaodias@...gle.com,
        jhubbard@...dia.com, willy@...radead.org
Subject: Re: [PATCH v4] mm: cma: support sysfs

On 04.03.21 17:17, Minchan Kim wrote:
> Since CMA is getting used more widely, it's more important to
> keep monitoring CMA statistics for system health since it's
> directly related to user experience.
> 
> This patch introduces sysfs statistics for CMA, in order to provide
> some basic monitoring of the CMA allocator.
> 
>   * the number of CMA page allocation attempts
>   * the number of CMA page allocation failures
> 
> These two values allow the user to calcuate the allocation
> failure rate for each CMA area.
> 
> e.g.)
>    /sys/kernel/mm/cma/WIFI/cma_alloc_pages_[attempts|fails]
>    /sys/kernel/mm/cma/SENSOR/cma_alloc_pages_[attempts|fails]
>    /sys/kernel/mm/cma/BLUETOOTH/cma_alloc_pages_[attempts|fails]
> 
> The cma_stat was intentionally allocated by dynamic allocation
> to harmonize with kobject lifetime management.
> https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@kroah.com/
> 
> Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Reviewed-by: John Hubbard <jhubbard@...dia.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  From v3 - https://lore.kernel.org/linux-mm/20210303205053.2906924-1-minchan@kernel.org/
>   * kmalloc_array - akpm
>   * add why cma_stat was implemented by dynamic allocation - akpm
>   * use !__GFP_NOWARN facility to print error - akpm
> 
>  From v2 - https://lore.kernel.org/linux-mm/20210208180142.2765456-1-minchan@kernel.org/
>   * sysfs doc and description modification - jhubbard
> 
>  From v1 - https://lore.kernel.org/linux-mm/20210203155001.4121868-1-minchan@kernel.org/
>   * fix sysfs build and refactoring - willy
>   * rename and drop some attributes - jhubbard
> 
>   Documentation/ABI/testing/sysfs-kernel-mm-cma |  25 ++++
>   mm/Kconfig                                    |   7 ++
>   mm/Makefile                                   |   1 +
>   mm/cma.c                                      |   6 +-
>   mm/cma.h                                      |  18 +++
>   mm/cma_sysfs.c                                | 110 ++++++++++++++++++
>   6 files changed, 166 insertions(+), 1 deletion(-)
>   create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-cma
>   create mode 100644 mm/cma_sysfs.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-cma b/Documentation/ABI/testing/sysfs-kernel-mm-cma
> new file mode 100644
> index 000000000000..f518af819cee
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-kernel-mm-cma
> @@ -0,0 +1,25 @@
> +What:		/sys/kernel/mm/cma/
> +Date:		Feb 2021
> +Contact:	Minchan Kim <minchan@...nel.org>
> +Description:
> +		/sys/kernel/mm/cma/ contains a subdirectory for each CMA
> +		heap name (also sometimes called CMA areas).
> +
> +		Each CMA heap subdirectory (that is, each
> +		/sys/kernel/mm/cma/<cma-heap-name> directory) contains the
> +		following items:
> +
> +			cma_alloc_pages_attempts
> +			cma_alloc_pages_fails

Nit: why "cma_" again when we are already under "/cma/" ?

I'd simply go with something like

"total_alloc_attempts"
"failed_alloc_attempts"

But maybe this has been discussed already.

> +
> +What:		/sys/kernel/mm/cma/<cma-heap-name>/cma_alloc_pages_attempts
> +Date:		Feb 2021
> +Contact:	Minchan Kim <minchan@...nel.org>
> +Description:
> +		the number of pages CMA API tried to allocate
> +
> +What:		/sys/kernel/mm/cma/<cma-heap-name>/cma_alloc_pages_fails
> +Date:		Feb 2021
> +Contact:	Minchan Kim <minchan@...nel.org>
> +Description:
> +		the number of pages CMA API failed to allocate

This will be useful.

-- 
Thanks,

David / dhildenb