linux-kernel - Re: [PATCH RFC v3 07/35] mm: cma: Add CMA_RELEASE

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Date: Wed, 31 Jan 2024 11:29:39 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Alexandru Elisei <alexandru.elisei@....com>
Cc: catalin.marinas@....com, will@...nel.org, oliver.upton@...ux.dev,
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Subject: Re: [PATCH RFC v3 07/35] mm: cma: Add CMA_RELEASE_{SUCCESS,FAIL}
 events



On 1/29/24 17:23, Alexandru Elisei wrote:
> Hi,
> 
> On Mon, Jan 29, 2024 at 03:01:24PM +0530, Anshuman Khandual wrote:
>>
>> On 1/25/24 22:12, Alexandru Elisei wrote:
>>> Similar to the two events that relate to CMA allocations, add the
>>> CMA_RELEASE_SUCCESS and CMA_RELEASE_FAIL events that count when CMA pages
>>> are freed.
>> How is this is going to be beneficial towards analyzing CMA alloc/release
>> behaviour - particularly with respect to this series. OR just adding this
>> from parity perspective with CMA alloc side counters ? Regardless this
>> CMA change too could be discussed separately.
> Added for parity and because it's useful for this series (see my reply to
> the previous patch where I discuss how I've used the counters).

As mentioned earlier, a new CONFIG_CMA_SYSFS element 'cma->nr_freed_pages'
could be instrumented in cma_release()'s success path for this purpose.
But again the failure path is not of much value as it could only happen
when there is an invalid input from the caller i.e when cma_pages_valid()
check fails.