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s=arc-20220608; d=hostedemail.com; t=1706676022; a=rsa-sha256; cv=none; b=qHkiQtOIC6nBiCgxLVzFFZ41wqd14w6RYqFudDb6WD7ARKOtcdZ3ZSYHkCJvJDHx3sUELQ cTefAsW5mPAnuVDHPsvlVlUQSRGFdtYfkYOnbLAgt3nPX0L9WjqWVs75R6ZaxrfijviLwS UEhmhKS0hFCAReVupuiRYq/7knsQXV8= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=none; spf=pass (imf03.hostedemail.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com; dmarc=pass (policy=none) header.from=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E4E6CDA7; Tue, 30 Jan 2024 20:41:03 -0800 (PST) Received: from [10.163.41.195] (unknown [10.163.41.195]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 52C333F738; Tue, 30 Jan 2024 20:40:06 -0800 (PST) Message-ID: <8cd39b48-7fb8-40b2-8d6c-e6fc2b48f86d@arm.com> Date: Wed, 31 Jan 2024 10:10:05 +0530 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 Cc: 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, 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> <0a71c87a-ae2c-4a61-8adb-3a51d6369b99@arm.com> <2cb8288c-5378-4968-a75b-8462b41998c6@arm.com> From: Anshuman Khandual In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: BC9F720015 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: hicsixud7154135hmncszstwkaru7uqf X-HE-Tag: 1706676021-210526 X-HE-Meta: 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 48wGdZAP YlpzfwsUjJdq8+KYZ1kjUCz8wIkRSdc1TlRbYhiIHH0xox9Ikyhbxa4uYOINQ1mJrO3XFKFAxR8yFiaCUpAzTpBC97jjKN5AvWx6RupvKYmqmil73h/oBWgm2QuLr+ZZ9KoEaFIfPzycl/w1ty+zNwTXh7vXMH7us0P4auXLdvW2mWRmKix8DQNuVyzHhPLF+5w9HXrUM5OwXaEt71h+yt3iCCMfy6NbIdpquMGWqN5l7heSRlradRDL3d9fo+RQQyXMa X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/30/24 17:28, Alexandru Elisei wrote: > Hi, > > On Tue, Jan 30, 2024 at 10:22:11AM +0530, Anshuman Khandual wrote: >> >> On 1/29/24 17:21, Alexandru Elisei wrote: >>> Hi, >>> >>> On Mon, Jan 29, 2024 at 02:54:20PM +0530, Anshuman Khandual wrote: >>>> >>>> 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 >>>>> --- >>>>> 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. >>> Having the number of CMA pages allocated and the number of CMA pages freed >>> allows someone to infer how many tagged pages are in use at a given time: >> That should not be done in CMA which is a generic multi purpose allocator. > Ah, ok. Let me rephrase that: Having the number of CMA pages allocated, the > number of failed CMA page allocations and the number of freed CMA pages > allows someone to infer how many CMA pages are in use at a given time. > That's valuable information for software designers and system > administrators, as it allows them to tune the number of CMA pages available > in a system. > > Or put another way: what would you consider to be more useful? Knowing the > number of cma_alloc()/cma_release() calls, or knowing the number of pages > that cma_alloc()/cma_release() allocated or freed? There is still value in knowing how many times cma_alloc() succeeded or failed regardless of the cumulative number pages involved over the time. Actually the count helps to understand how cma_alloc() performed overall as an allocator. But on the cma_release() path there is no chances of failure apart from - just when the caller itself provides an wrong input. So there are no corresponding CMA_RELEASE_SUCCESS/CMA_RELEASE_FAIL vmstat counters in there - for a reason ! Coming back to CMA based pages being allocated and freed, there is already an interface via sysfs (CONFIG_CMA_SYSFS) which gets updated in cma_alloc() path via cma_sysfs_account_success_pages() and cma_sysfs_account_fail_pages(). #ls /sys/kernel/mm/cma/ alloc_pages_fail alloc_pages_success Why these counters could not meet your requirements ? Also 'struct cma' can be updated to add an element 'nr_pages_freed' to be tracked in cma_release(), providing free pages count as well. There are additional debug fs based elements (CONFIG_CMA_DEBUGFS) available. #ls /sys/kernel/debug/cma/ alloc base_pfn bitmap count free maxchunk order_per_bit used