linux-kernel - Re: [PATCH] mm/cma: Add sysfs file 'release_pages

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Message-Id: <20240206093857.d834af4f96d643c53e29e02d@linux-foundation.org>
Date: Tue, 6 Feb 2024 09:38:57 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: linux-mm@...ck.org, alexandru.elisei@....com,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/cma: Add sysfs file 'release_pages_success'

On Tue,  6 Feb 2024 10:27:31 +0530 Anshuman Khandual <anshuman.khandual@....com> wrote:

> This adds the following new sysfs file tracking the number of successfully
> released pages from a given CMA heap area. Also like before - this will be
> available via CONFIG_CMA_SYSFS, and help in determining active CMA pages
> available on the system.

"like before" is mysterious.  Is this referring to some other patch? 
To existing code?  Please be explicit and complete.

> /sys/kernel/mm/cma/<cma-heap-area>/release_pages_success
> 
> It adds an element 'nr_pages_released' (with CONFIG_CMA_SYSFS config) into
> 'struct cma' which gets updated during cma_release().

The changelog doesn't explain why Linux needs this feature.  The value
to our users.  Perhaps that info is buried in the link which is buried
below the ^---$, but as this is the most important part of a changelog,
it really should be spelled out here, completely and carefully please.

> ---
> This patch applies on v6.8-rc3
> 
> Some earlier relevant discussions regarding arm64 MTE dynamic tag storage
> in this regard can be found here.
> 
> https://lore.kernel.org/all/ZbpKyNVHfhf1-AAv@raptor/