linux-kernel - Re: [PATCH RFC v3 06/35] mm: cma: Make CMA_ALLOC

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Date: Mon, 29 Jan 2024 14:54:20 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Alexandru Elisei <alexandru.elisei@....com>, catalin.marinas@....com,
 will@...nel.org, oliver.upton@...ux.dev, maz@...nel.org,
 james.morse@....com, suzuki.poulose@....com, yuzenghui@...wei.com,
 arnd@...db.de, akpm@...ux-foundation.org, mingo@...hat.com,
 peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
 mhiramat@...nel.org, rppt@...nel.org, hughd@...gle.com
Cc: pcc@...gle.com, steven.price@....com, vincenzo.frascino@....com,
 david@...hat.com, eugenis@...gle.com, kcc@...gle.com, hyesoo.yu@...sung.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 kvmarm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
 linux-arch@...r.kernel.org, linux-mm@...ck.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v3 06/35] mm: cma: Make CMA_ALLOC_SUCCESS/FAIL count
 the number of pages



On 1/25/24 22:12, Alexandru Elisei wrote:
> The CMA_ALLOC_SUCCESS, respectively CMA_ALLOC_FAIL, are increased by one
> after each cma_alloc() function call. This is done even though cma_alloc()
> can allocate an arbitrary number of CMA pages. When looking at
> /proc/vmstat, the number of successful (or failed) cma_alloc() calls
> doesn't tell much with regards to how many CMA pages were allocated via
> cma_alloc() versus via the page allocator (regular allocation request or
> PCP lists refill).
> 
> This can also be rather confusing to a user who isn't familiar with the
> code, since the unit of measurement for nr_free_cma is the number of pages,
> but cma_alloc_success and cma_alloc_fail count the number of cma_alloc()
> function calls.
> 
> Let's make this consistent, and arguably more useful, by having
> CMA_ALLOC_SUCCESS count the number of successfully allocated CMA pages, and
> CMA_ALLOC_FAIL count the number of pages the cma_alloc() failed to
> allocate.
> 
> For users that wish to track the number of cma_alloc() calls, there are
> tracepoints for that already implemented.
> 
> Signed-off-by: Alexandru Elisei <alexandru.elisei@....com>
> ---
>  mm/cma.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/cma.c b/mm/cma.c
> index f49c95f8ee37..dbf7fe8cb1bd 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -517,10 +517,10 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
>  	pr_debug("%s(): returned %p\n", __func__, page);
>  out:
>  	if (page) {
> -		count_vm_event(CMA_ALLOC_SUCCESS);
> +		count_vm_events(CMA_ALLOC_SUCCESS, count);
>  		cma_sysfs_account_success_pages(cma, count);
>  	} else {
> -		count_vm_event(CMA_ALLOC_FAIL);
> +		count_vm_events(CMA_ALLOC_FAIL, count);
>  		if (cma)
>  			cma_sysfs_account_fail_pages(cma, count);
>  	}

Without getting into the merits of this patch - which is actually trying to do
semantics change to /proc/vmstat, wondering how is this even related to this
particular series ? If required this could be debated on it's on separately.