From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3E38D13FE2; Wed, 31 Jan 2024 04:40:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706676024; cv=none; b=ZA/h1NV5hCIsbNV/kPGmZuyPuXxwNG14btxKk1BEcNL0dWOLRUUz11KvmvhDk+SEoP1jSXibxU70DdAtli2XYBIC6zNFf12Fcp79TNlJE4rawobxmfTSeWcY7rYtgRV0rRxo6Xim1AWY+ET/YVb2TQEq+gY/jtFLmi6d5BWZw9k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706676024; c=relaxed/simple; bh=3R14n/VzZcxmNnLweehoAPfyjB2o8LMMfTdOUihMJJY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=plDZY6P0eYCU92S/dlwxRLOVIieIscajYpzPOyvs14+QI+k5YJeJzW8OTc5LikRZrNsACTIz0VkZG9vmPRtxvx/mY0kddxErF2XOWomN7U3neoWywAbzEnm8X0UM0sVlND9nMmwlyhUgKAYKEVWcpY+g7wl3NG+iDk1RCR8jNl4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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