Received-SPF: pass (google.com: domain of linux-kernel+bounces-42434-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Message-ID: <0a71c87a-ae2c-4a61-8adb-3a51d6369b99@arm.com>
Date: Mon, 29 Jan 2024 14:54:20 +0530
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH RFC v3 06/35] mm: cma: Make CMA_ALLOC_SUCCESS/FAIL count
 the number of pages
Content-Language: en-US
To: Alexandru Elisei <alexandru.elisei@arm.com>, catalin.marinas@arm.com,
 will@kernel.org, oliver.upton@linux.dev, maz@kernel.org,
 james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com,
 arnd@arndb.de, akpm@linux-foundation.org, mingo@redhat.com,
 peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org,
 dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
 mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
 mhiramat@kernel.org, rppt@kernel.org, hughd@google.com
Cc: pcc@google.com, steven.price@arm.com, vincenzo.frascino@arm.com,
 david@redhat.com, eugenis@google.com, kcc@google.com, hyesoo.yu@samsung.com,
 linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
 kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org,
 linux-arch@vger.kernel.org, linux-mm@kvack.org,
 linux-trace-kernel@vger.kernel.org
References: <20240125164256.4147-1-alexandru.elisei@arm.com>
 <20240125164256.4147-7-alexandru.elisei@arm.com>
From: Anshuman Khandual <anshuman.khandual@arm.com>
In-Reply-To: <20240125164256.4147-7-alexandru.elisei@arm.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit


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@arm.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.