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(p200300cbc70b7b007c52a5fa800496fd.dip0.t-ipconnect.de. [2003:cb:c70b:7b00:7c52:a5fa:8004:96fd]) by smtp.gmail.com with ESMTPSA id p13-20020a5d4e0d000000b002f4cf72fce6sm15563321wrt.46.2023.04.19.04.09.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Apr 2023 04:09:37 -0700 (PDT) Message-ID: <54f24909-91b8-01cc-5a1f-6146ebc9297c@redhat.com> Date: Wed, 19 Apr 2023 13:09:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [RFC PATCH 03/26] mm: make pageblock_order 2M per default Content-Language: en-US To: Vlastimil Babka , Johannes Weiner , linux-mm@kvack.org Cc: Kaiyang Zhao , Mel Gorman , David Rientjes , linux-kernel@vger.kernel.org, kernel-team@fb.com, "Kirill A. Shutemov" References: <20230418191313.268131-1-hannes@cmpxchg.org> <20230418191313.268131-4-hannes@cmpxchg.org> <804dd674-6078-7455-8dda-1bd921bed828@suse.cz> From: David Hildenbrand Organization: Red Hat In-Reply-To: <804dd674-6078-7455-8dda-1bd921bed828@suse.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19.04.23 12:36, Vlastimil Babka wrote: > On 4/18/23 21:12, Johannes Weiner wrote: >> pageblock_order can be of various sizes, depending on configuration, >> but the default is MAX_ORDER-1. Given 4k pages, that comes out to >> 4M. This is a large chunk for the allocator/reclaim/compaction to try >> to keep grouped per migratetype. It's also unnecessary as the majority >> of higher order allocations - THP and slab - are smaller than that. > > Well in my experience the kernel usually has hugetlbfs config-enabled so it > uses 2MB pageblocks (on x86) even if hugetlbfs is unused at runtime and THP > is used instead. But sure, we can set a better default that's not tied to > hugetlbfs. As virtio-mem really wants small pageblocks (hot(un)plug granularity), I've seen reports from users without HUGETLB configured complaining about this (on x86, we'd get 4M instead of 2M). So having a better default (PMD_SIZE) sounds like a good idea to me (and I even recall suggesting to change the !hugetlb default). -- Thanks, David / dhildenb