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[2003:d8:2f18:f900:e0ae:65d5:8bf8:8cfd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45e017c0643sm172762125e9.23.2025.09.15.04.45.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Sep 2025 04:45:42 -0700 (PDT) Message-ID: <6ec80746-2945-485f-930e-8cc34446f9e3@redhat.com> Date: Mon, 15 Sep 2025 13:45:39 +0200 Precedence: bulk X-Mailing-List: linux-trace-kernel@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: <155c821d-402c-4627-a723-6f8c88a2f65c@lucifer.local> <2757fb07-78bf-4a39-8c60-8ca8be200994@lucifer.local> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 15.09.25 13:35, Lorenzo Stoakes wrote: > On Mon, Sep 15, 2025 at 01:29:22PM +0200, David Hildenbrand wrote: >> On 15.09.25 13:23, Lorenzo Stoakes wrote: >>> On Mon, Sep 15, 2025 at 01:14:32PM +0200, David Hildenbrand wrote: >>>> On 15.09.25 13:02, Lorenzo Stoakes wrote: >>>>> On Mon, Sep 15, 2025 at 12:52:03PM +0200, David Hildenbrand wrote: >>>>>> On 15.09.25 12:43, Lorenzo Stoakes wrote: >>>>>>> On Mon, Sep 15, 2025 at 12:22:07PM +0200, David Hildenbrand wrote: >>>>>>>> >>>>>>>> 0 -> ~100% used (~0% none) >>>>>>>> 1 -> ~50% used (~50% none) >>>>>>>> 2 -> ~25% used (~75% none) >>>>>>>> 3 -> ~12.5% used (~87.5% none) >>>>>>>> 4 -> ~11.25% used (~88,75% none) >>>>>>>> ... >>>>>>>> 10 -> ~0% used (~100% none) >>>>>>> >>>>>>> Oh and shouldn't this be inverted? >>>>>>> >>>>>>> 0 eagerness = we eat up all none PTE entries? Isn't that pretty eager? :P >>>>>>> 10 eagerness = we aren't eager to eat up none PTE entries at all? >>>>>>> >>>>>>> Or am I being dumb here? >>>>>> >>>>>> Good question. >>>>>> >>>>>> For swappiness it's: 0 -> no swap (conservative) >>>>>> >>>>>> So intuitively I assumed: 0 -> no pte_none (conservative) >>>>>> >>>>>> You're the native speaker, so you tell me :) >>>>> >>>>> To me this is about 'eagerness to consume empty PTE entries' so 10 is more >>>>> eager, 0 is not eager at all, i.e. inversion of what you suggest :) >>>> >>>> Just so we are on the same page: it is about "eagerness to collapse", right? >>>> >>>> Wouldn't a 0 mean "I am not eager, I will not waste any memory, I am very >>>> careful and bail out on any pte_none" vs. 10 meaning "I am very eager, I >>>> will collapse no matter what I find in the page table, waste as much memory >>>> as I want"? >>> >>> Yeah, this is my understanding of your scale, or is my understanding also >>> inverted? :) >>> >>> Right now it's: >>> >>> eagerness max_ptes_none >>> >>> 0 -> 511 >>> ... >>> 10 -> 0 >>> >>> Right? >> >> Just so we are on the same page, this is what I had: >> >> 0 -> ~100% used (~0% none) >> >> So "0" -> 0 pte_none or 512 used. >> >> (note the used vs. none) > > OK right so we're talking about the same thing, I guess? > > I was confused partly becuase of the scale, becuase weren't people setting > this parameter to low values in practice? > > And now we make it so we have equivalent of: > > 0 -> 0 > 1 -> 256 > 2 -> 384 Ah, there is the problem, that's not what I had in mind. 0 -> ~100% used (~0% none) ... 8 -> ~87,5% used (~12.5% none) 9 -> ~75% used (~25% none) 9 -> ~50% used (~50% none) 10 -> ~0% used (~100% none) Hopefully I didn't mess it up again. -- Cheers David / dhildenb