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[2003:d8:2f09:3f00:d228:bd67:7baa:d604]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4290c7728c5sm76115605e9.32.2024.08.09.06.15.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 09 Aug 2024 06:15:47 -0700 (PDT) Message-ID: <8258bf4c-ecec-4e06-ada0-da9fb99b1219@redhat.com> Date: Fri, 9 Aug 2024 15:15:46 +0200 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 v2] mm: Override mTHP "enabled" defaults at kernel cmdline To: Ryan Roberts , Barry Song Cc: Andrew Morton , Jonathan Corbet , Lance Yang , Baolin Wang , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240808101700.571701-1-ryan.roberts@arm.com> <99b78488-c524-4269-b1fb-a13eaa4f274c@redhat.com> <75eb6e75-8a6d-460a-8e96-7496ed1396b7@redhat.com> <3c8f00ea-af28-46c7-9a5d-83c4b9462be3@arm.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit >>>>> -You can change the sysfs boot time defaults of Transparent Hugepage >>>>> -Support by passing the parameter ``transparent_hugepage=always`` or >>>>> -``transparent_hugepage=madvise`` or ``transparent_hugepage=never`` >>>>> -to the kernel command line. >>>>> +You can change the sysfs boot time default for the top-level "enabled" >>>>> +control by passing the parameter ``transparent_hugepage=always`` or >>>>> +``transparent_hugepage=madvise`` or ``transparent_hugepage=never`` to the >>>>> +kernel command line. >>>>> + >>>>> +Alternatively, each supported anonymous THP size can be controlled by >>>>> +passing ``thp_anon=[KMG]:``, where ```` is the THP size >>>>> +and ```` is one of ``always``, ``madvise``, ``never`` or >>>>> +``inherit``. >>>>> + >>>>> +For example, the following will set 64K THP to ``always``:: >>>>> + >>>>> +     thp_anon=64K:always >>>>> + >>>>> +``thp_anon=`` may be specified multiple times to configure all THP sizes as >>>>> +required. If ``thp_anon=`` is specified at least once, any anon THP sizes >>>>> +not explicitly configured on the command line are implicitly set to >>>>> +``never``. >>>> >>>> I suggest documenting that "thp_anon=" will not effect the value of >>>> "transparent_hugepage=", or any configured default. > > Did you see the previous conversation with Barry about whether or not to honour > configured defaults when any thp_anon= is provided [1]? Sounds like you also > think we should honour the PMD "inherit" default if not explicitly provided on > the command line? (see link for justification for the approach I'm currently > taking). I primarily think that we should document it :) What if someone passes "transparent_hugepage=always" and "thp_anon=..."? I would assume that transparent_hugepage would only affect the global toggle then? > > [1] > https://lore.kernel.org/linux-mm/CAGsJ_4x8ruPspuk_FQVggJMWcXLbRuZFq44gg-Dt7Ewt3ExqTw@mail.gmail.com/ > >>>> >>>> Wondering if a syntax like >>>> >>>> thp_anon=16K,32K,64K:always;1048K,2048K:madvise > > Are there examples of that syntax already or have you just made it up? I found > examples with the colon (:) but nothing this fancy. I guess that's not a reason > not to do it though (other than the risk of screwing up the parser in a subtle way). I made it up -- mostly ;) I think we are quite flexible on what we can do. As always, maybe we can keep it bit consistent with existing stuff. For hugetlb_cma we have things like ":nn[KMGTPE|[,:nn[KMGTPE]] "memmap=" options are more ... advanced, including memory ranges. There are a bunch more documented in kernel-parameters.txt that have more elaborate formats. Ranges would probably be the most valuable addition. So maybe we should start with: thp_anon=16K-64K:always,1048K-2048K:madvise So to enable all THPs it would simply be thp_anon=16K-2M:always Interesting question what would happen if someone passes: thp_anon=8K-2M:always Likely we simply would apply it to any size in the range, even if start/end is not a THP size. But we would want to complain to the user if someone only specifies a single one (or a range does not even select a single one) that does not exist: thp_anon=8K:always > >>>> >>>> (one could also support ranges, like "16K-64K") >>>> >>>> Would be even better. Then, maybe only allow a single instance. >>>> >>>> Maybe consider it if it's not too crazy to parse ;) > I'll take a look. I'm going to be out for 3 weeks from end of Monday though, so Oh, lucky you! Enjoy! > probably won't get around to that until I'm back. I know Barry is keen to get > this merged, so Barry, if you'd like to take it over that's fine by me (I'm sure > you have enough on your plate though). -- Cheers, David / dhildenb