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[2003:cb:c714:c00:b08b:a871:ce99:dfde]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3680dabf3bdsm11219746f8f.30.2024.07.17.03.03.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 Jul 2024 03:03:45 -0700 (PDT) Message-ID: Date: Wed, 17 Jul 2024 12:03:44 +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 v1 2/2] mm: mTHP stats for pagecache folio allocations To: Ryan Roberts , Lance Yang , Baolin Wang Cc: Andrew Morton , Hugh Dickins , Jonathan Corbet , "Matthew Wilcox (Oracle)" , Barry Song , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240711072929.3590000-1-ryan.roberts@arm.com> <20240711072929.3590000-3-ryan.roberts@arm.com> <9e0d84e5-2319-4425-9760-2c6bb23fc390@linux.alibaba.com> <756c359e-bb8f-481e-a33f-163c729afa31@redhat.com> <8c32a2fc-252d-406b-9fec-ce5bab0829df@arm.com> <5c58d9ea-8490-4ae6-b7bf-be816dab3356@redhat.com> <9052f430-2c5a-4d9d-b54c-bd093b797702@redhat.com> <5472faf5-1fbe-4a89-a17e-83716fc00b5a@redhat.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 >>>>> >>>>> But today, controls and stats are exposed for: >>>>> >>>>>     anon: >>>>>       min order: 2 >>>>>       max order: PMD_ORDER >>>>>     anon-shmem: >>>>>       min order: 2 >>>>>       max order: PMD_ORDER >>>>>     tmpfs-shmem: >>>>>       min order: PMD_ORDER >>>>>       max order: PMD_ORDER >>>>>     file: >>>>>       min order: Nothing yet (this patch proposes 1) >>>>>       max order: Nothing yet (this patch proposes MAX_PAGECACHE_ORDER) >>>>> >>>>> So I think there is definitely a bug for shmem where the minimum order control >>>>> should be order-1 but its currently order-2. >>>> >>>> Maybe, did not play with that yet. Likely order-1 will work. (although probably >>>> of questionable use :) ) >>> >>> You might have to expand on why its of "questionable use". I'd assume it has the >>> same amount of value as using order-1 for regular page cache pages? i.e. half >>> the number of objects to manage for the same amount of memory. >> >> order-1 was recently added for the pagecache to get some device setups running >> (IIRC, where we cannot use order-0, because device blocksize > PAGE_SIZE). >> >> You might be right about "half the number of objects", but likely just going for >> order-2, order-3, order-4 ... for shmem might be even better. And simply falling >> back to order-0 when you cannot get the larger orders. > > Sure, but then you're into the territory of baking in policy. Remember that > originally I was only interested in 64K but the concensus was to expose all the > sizes. Same argument applies to 8K; expose it and let others decide policy. I don't disagree. The point I'm trying to make is that there was so far there was no strong evidence that it is really required. Support for the pagecache had a different motivation for these special devices. But again, I agree that we should just make it consistent and allow for it. :) -- Cheers, David / dhildenb