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[2003:d8:2f18:f900:e0ae:65d5:8bf8:8cfd]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e8c7375fb7sm9147411f8f.14.2025.09.15.04.10.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Sep 2025 04:10:24 -0700 (PDT) Message-ID: <1312fa3e-88dd-490a-9e07-9749c625933b@redhat.com> Date: Mon, 15 Sep 2025 13:10:22 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 00/15] khugepaged: mTHP support To: Lorenzo Stoakes Cc: Kiryl Shutsemau , Nico Pache , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org, baohua@kernel.org, willy@infradead.org, peterx@redhat.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, yang@os.amperecomputing.com, aarcange@redhat.com, raquini@redhat.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, tiwai@suse.de, will@kernel.org, dave.hansen@linux.intel.com, jack@suse.cz, cl@gentwo.org, jglisse@google.com, surenb@google.com, zokeefe@google.com, hannes@cmpxchg.org, rientjes@google.com, mhocko@suse.com, rdunlap@infradead.org, hughd@google.com, richard.weiyang@gmail.com, lance.yang@linux.dev, vbabka@suse.cz, rppt@kernel.org, jannh@google.com, pfalcato@suse.de References: <2c5328ee-fb6e-45cf-a151-868cc8e7ff97@lucifer.local> <4508810d-7645-4f57-a0c5-2ee9f44206fc@lucifer.local> <34754ca4-fced-4a3c-8ff8-c00967d487de@redhat.com> <92352257-5be4-4aaa-b97f-c4e879ac6959@lucifer.local> <5099d9fe-4a07-4acd-95c8-782ffc74df37@lucifer.local> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 15.09.25 12:59, Lorenzo Stoakes wrote: > On Mon, Sep 15, 2025 at 12:52:53PM +0200, David Hildenbrand wrote: >> On 15.09.25 12:48, Lorenzo Stoakes wrote: >>> On Mon, Sep 15, 2025 at 12:44:34PM +0200, David Hildenbrand wrote: >>>>>>> Mapping that to actual THP sizes (#pages in a thp) on an arch will be easy. >>>>>> >>>>>> And at different mTHP levels too right? >>>>>> >>>>> >>>>> Another point here, since we have to keep: >>>>> >>>>> /sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_none >>>>> >>>>> Around, and users will try to set values there, presumably we will now add: >>>>> >>>>> /sys/kernel/mm/transparent_hugepage/khugepaged/eagerness >>>>> >>>>> How will we map <-> the two tunables? >>>> >>>> Well, the easy case if someone updates eagerness, then we simply et it to >>>> whatever magic value we compute and document. >>>> >>>> The other direction is more problematic, likely we'll simply warn and do >>>> something reasonable (map it to whatever eagerness scale is closest or >>>> simply indicate it as "-1" -- user intervened or sth like that) >>> >>> I don't love the idea of a -1 situation, as that's going to create some >>> confusion. >> >> swapiness also has a "max" parameter, so we could just say "override" /" >> disabled" / whatever? > > I don't love the user being able to override this though, let's just nuke their > ability to set this pleeeease. > > Because if they can override it, then we have to do some deeply nasty scaling > for mTHP again. There are ways to have it working internally, just using a different "scale" instead of the 100 -> 50 -> 25 etc. I am afraid we cannot change the parameter to ignore other values because of the interaction with the shrinker that easily .... we might be able to detracted at wait a bunch of kernel releases probably. -- Cheers David / dhildenb