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s=arc-20220608; d=hostedemail.com; t=1704884160; a=rsa-sha256; cv=none; b=YXqqgohhZF8PtyQ7wefidMTLUo6LFVMf+w71ktNSPds73q67Wj4slz7s6FEUPROl7X+7cS Ps2cU5Q66JWVZgbsmEGXimWd3R3zPZ7i3GRaLDbFAlN1i7IRFKiAvRC4NColMGJ5h/Jhag iGpBLX5s4Rmwto+bY+2mOT5ZUZIygVU= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=none; spf=pass (imf30.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@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 346C02F4; Wed, 10 Jan 2024 02:56:45 -0800 (PST) Received: from [10.57.76.12] (unknown [10.57.76.12]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 153EE3F64C; Wed, 10 Jan 2024 02:55:57 -0800 (PST) Message-ID: <974a2670-7fa9-425e-921e-8d54a596e6cf@arm.com> Date: Wed, 10 Jan 2024 10:55:56 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1] tools/mm: Add thpmaps script to dump THP usage info Content-Language: en-GB To: David Hildenbrand , Barry Song <21cnbao@gmail.com> Cc: John Hubbard , Andrew Morton , Zenghui Yu , Matthew Wilcox , Kefeng Wang , Zi Yan , Alistair Popple , linux-mm@kvack.org References: <20240102153828.1002295-1-ryan.roberts@arm.com> <4e7445a0-acc9-487f-999f-a2b6d03d265e@nvidia.com> <3bd5e4a3-9f67-4483-9a0e-9abb5eb783cd@arm.com> <94ebe62b-5f55-4be9-b464-4105b4692496@arm.com> <68d5ce7e-6587-47c6-bd0f-988adf5d92a4@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: 868uik8o8hci8bjygehueghfqffx7gf1 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 8C2FD80016 X-Rspam-User: X-HE-Tag: 1704884160-436534 X-HE-Meta: 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 cOVc8Vk5 WN4Za7vz2htBy22q4I8n/ij9y37cpAxbim4BqoTGOySUMFWbJd/kGJoTwiKRpsWF9M3rZvVbmS4khoAF7Z53Cc84w14LPd5pfHK5coH/XBjugM4qnPt13fAbL38X0o2JMgfchLSUupKSsnrz3QVgLnk2Uj+j+I9xPt+jVvzMyJs4ClNHNMwr2scClNxpqZNWuUc0zWQQv8ltWuSF5AeGPbWoWVGBSVstfGcgw 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 10/01/2024 10:42, David Hildenbrand wrote: > On 10.01.24 11:38, Ryan Roberts wrote: >> On 10/01/2024 10:30, Barry Song wrote: >>> On Wed, Jan 10, 2024 at 6:23 PM Ryan Roberts wrote: >>>> >>>> On 10/01/2024 09:09, Barry Song wrote: >>>>> On Wed, Jan 10, 2024 at 4:58 PM Ryan Roberts wrote: >>>>>> >>>>>> On 10/01/2024 08:02, Barry Song wrote: >>>>>>> On Wed, Jan 10, 2024 at 12:16 PM John Hubbard wrote: >>>>>>>> >>>>>>>> On 1/9/24 19:51, Barry Song wrote: >>>>>>>>> On Wed, Jan 10, 2024 at 11:35 AM John Hubbard wrote: >>>>>>>> ... >>>>>>>>>> Hi Ryan, >>>>>>>>>> >>>>>>>>>> One thing that immediately came up during some recent testing of mTHP >>>>>>>>>> on arm64: the pid requirement is sometimes a little awkward. I'm running >>>>>>>>>> tests on a machine at a time for now, inside various containers and >>>>>>>>>> such, and it would be nice if there were an easy way to get some numbers >>>>>>>>>> for the mTHPs across the whole machine. >>>>>> >>>>>> Just to confirm, you're expecting these "global" stats be truely global >>>>>> and not >>>>>> per-container? (asking because you exploicitly mentioned being in a >>>>>> container). >>>>>> If you want per-container, then you can probably just create the container >>>>>> in a >>>>>> cgroup? >>>>>> >>>>>>>>>> >>>>>>>>>> I'm not sure if that changes anything about thpmaps here. Probably >>>>>>>>>> this is fine as-is. But I wanted to give some initial reactions from >>>>>>>>>> just some quick runs: the global state would be convenient. >>>>>> >>>>>> Thanks for taking this for a spin! Appreciate the feedback. >>>>>> >>>>>>>>> >>>>>>>>> +1. but this seems to be impossible by scanning pagemap? >>>>>>>>> so may we add this statistics information in kernel just like >>>>>>>>> /proc/meminfo or a separate /proc/mthp_info? >>>>>>>>> >>>>>>>> >>>>>>>> Yes. From my perspective, it looks like the global stats are more useful >>>>>>>> initially, and the more detailed per-pid or per-cgroup stats are the >>>>>>>> next level of investigation. So feels odd to start with the more >>>>>>>> detailed stats. >>>>>>>> >>>>>>> >>>>>>> probably because this can be done without the modification of the kernel. >>>>>> >>>>>> Yes indeed, as John said in an earlier thread, my previous attempts to add >>>>>> stats >>>>>> directly in the kernel got pushback; DavidH was concerned that we don't >>>>>> really >>>>>> know exectly how to account mTHPs yet >>>>>> (whole/partial/aligned/unaligned/per-size/etc) so didn't want to end up >>>>>> adding >>>>>> the wrong ABI and having to maintain it forever. There has also been some >>>>>> pushback regarding adding more values to multi-value files in sysfs, so David >>>>>> was suggesting coming up with a whole new scheme at some point (I know >>>>>> /proc/meminfo isn't sysfs, but the equivalent files for NUMA nodes and >>>>>> cgroups >>>>>> do live in sysfs). >>>>>> >>>>>> Anyway, this script was my attempt to 1) provide a short term solution to the >>>>>> "we need some stats" request and 2) provide a context in which to explore >>>>>> what >>>>>> the right stats are - this script can evolve without the ABI problem. >>>>>> >>>>>>> The detailed per-pid or per-cgroup is still quite useful to my case in which >>>>>>> we set mTHP enabled/disabled and allowed sizes according to vma types, >>>>>>> eg. libc_malloc, java heaps etc. >>>>>>> >>>>>>> Different vma types can have different anon_name. So I can use the detailed >>>>>>> info to find out if specific VMAs have gotten mTHP properly and how many >>>>>>> they have gotten. >>>>>>> >>>>>>>> However, Ryan did clearly say, above, "In future we may wish to >>>>>>>> introduce stats directly into the kernel (e.g. smaps or similar)". And >>>>>>>> earlier he ran into some pushback on trying to set up /proc or /sys >>>>>>>> values because this is still such an early feature. >>>>>>>> >>>>>>>> I wonder if we could put the global stats in debugfs for now? That's >>>>>>>> specifically supposed to be a "we promise *not* to keep this ABI stable" >>>>>>>> location. >>>>>> >>>>>> Now that I think about it, I wonder if we can add a --global mode to the >>>>>> script >>>>>> (or just infer global when neither --pid nor --cgroup are provided). I >>>>>> think I >>>>>> should be able to determine all the physical memory ranges from /proc/iomem, >>>>>> then grab all the info we need from /proc/kpageflags. We should then be >>>>>> able to >>>>>> process it all in much the same way as for --pid/--cgroup and provide the >>>>>> same >>>>>> stats, but it will apply globally. What do you think? >>>> >>>> Having now thought about this for a few mins (in the shower, if anyone wants >>>> the >>>> complete picture :) ), this won't quite work. This approach doesn't have the >>>> virtual mapping information so the best it can do is tell us "how many of each >>>> size of THP are allocated?" - it doesn't tell us anything about whether they >>>> are >>>> fully or partially mapped or what their alignment is (all necessary if we want >>>> to know if they are contpte-mapped). So I don't think this approach is going to >>>> be particularly useful. >>>> >>>> And this is also the big problem if we want to gather stats inside the kernel; >>>> if we want something equivalant to /proc/meminfo's >>>> AnonHugePages/ShmemPmdMapped/FilePmdMapped, we need to consider not just the >>>> allocation of the THP but also whether it is mapped. That's easy for >>>> PMD-mappings, because there is only one entry to consider - when you set it, >>>> you >>>> increment the number of PMD-mapped THPs, when you clear it, you decrement. But >>>> for PTE-mappings it's harder; you know the size when you are mapping so its >>>> easy >>>> to increment, but you can do a partial unmap, so you would need to scan the >>>> PTEs >>>> to figure out if we are unmapping the first page of a previously >>>> fully-PTE-mapped THP, which is expensive. We would need a cheap mechanism to >>>> determine "is this folio fully and contiguously mapped in at least one >>>> process?". >>> >>> as OPPO's approach I shared to you before is maintaining two mapcount >>> 1. entire map >>> 2. subpage's map >>> 3. if 1 and 2 both exist, it is DoubleMapped. >>> >>> This isn't a problem for us. and everytime if we do a partial unmap, >>> we have an explicit >>> cont_pte split which will decrease the entire map and increase the >>> subpage's mapcount. >>> >>> but its downside is that we expose this info to mm-core. >> >> OK, but I think we have a slightly more generic situation going on with the >> upstream; If I've understood correctly, you are using the PTE_CONT bit in the >> PTE to determne if its fully mapped? That works for your case where you only >> have 1 size of THP that you care about (contpte-size). But for the upstream, we >> have multi-size THP so we can't use the PTE_CONT bit to determine if its fully >> mapped because we can only use that bit if the THP is at least 64K and aligned, >> and only on arm64. We would need a SW bit for this purpose, and the mm would >> need to update that SW bit for every PTE one the full -> partial map transition. > > Oh no. Let's not make everything more complicated for the purpose of some stats. > Indeed, I was intending to argue *against* doing it this way. Fundamentally, if we want to know what's fully mapped and what's not, then I don't see any way other than by scanning the page tables and we might as well do that in user space with this script. Although, I expect you will shortly make a proposal that is simple to implement and prove me wrong ;-)