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Shutemov" Cc: linux-mm@kvack.org, Kaiyang Zhao , Mel Gorman , Vlastimil Babka , David Rientjes , linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [RFC PATCH 03/26] mm: make pageblock_order 2M per default Message-ID: <20230419034404.GA274690@cmpxchg.org> References: <20230418191313.268131-1-hannes@cmpxchg.org> <20230418191313.268131-4-hannes@cmpxchg.org> <20230419000105.matz43p6ihrqmado@box.shutemov.name> <20230419025552.GB272256@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230419025552.GB272256@cmpxchg.org> X-Stat-Signature: 6tw78on77p6p94wjapkuxmemci1g57nj X-Rspam-User: X-Rspamd-Queue-Id: D400C1A000F X-Rspamd-Server: rspam06 X-HE-Tag: 1681875846-217069 X-HE-Meta: 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 uGKEzssK 5EK4OsSwrh2s8tkjELz6IvZ3lTwZsxtpNqIrZ1W0ipWlpgJTOQOTKiMzLgvjQJ70ixfyifcsBAxUzArN2wPOk1YgwW7tO63mhho5q4wXr7rjWbX6sSUoGdmrLbNmeQ1w0Da4KPR9gdmqG4G1QS6l0aWtLO6ZRH1+ok+AslW7cTGh0Tvpp/excg7e7jsyhdITC+umM7FvLGxjy5uTL0eB6M/QtmChkuucyHoPPkXJhdDh2IH7yXr8CKAu4I1oFo7cI2+5saPZu3Dkl38+D2uNA6nkpgGksmH6YMCCDdbJFafxaqbia2mMJk1tLL3C7T1BHSrQuc5poErJ0THN7JVXGyEQ4q4U+89LnMq/Oe7MN5ObckE+YL/OVh7UKcPicBBL5kRAD4gzxechf+4AA1GNxCqAhSPAK8IGXx1OXxhThx7oT310NFrQavnEiy5LvMwmE69I/mHQ4LrmHgotmq1dmwWo4w338vIe/3iOQXR+nR+S0wA0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Apr 18, 2023 at 10:55:53PM -0400, Johannes Weiner wrote: > On Wed, Apr 19, 2023 at 03:01:05AM +0300, Kirill A. Shutemov wrote: > > On Tue, Apr 18, 2023 at 03:12:50PM -0400, Johannes Weiner wrote: > > > pageblock_order can be of various sizes, depending on configuration, > > > but the default is MAX_ORDER-1. > > > > Note that MAX_ORDER got redefined in -mm tree recently. > > > > > 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. > > > > This seems way to x86-specific. > > Other arches have larger THP sizes. I believe 16M is common. > > > > Maybe define it as min(MAX_ORDER, PMD_ORDER)? > > Hm, let me play around with larger pageblocks. > > The thing that gives me pause is that this seems quite aggressive as a > default block size for the allocator and reclaim/compaction - if you > consider the implications for internal fragmentation and the amount of > ongoing defragmentation work it would require. > > IOW, it's not just a function of physical page size supported by the > CPU. It's also a function of overall memory capacity. Independent of > architecture, 2MB seems like a more reasonable step up than 16M. [ Quick addition: on those other archs, these patches would still help with other, non-THP sources of compound allocations, such as slub, variable-order cache folios, and really any orders up to 2M. So it's not like we *have* to raise it to PMD_ORDER for them to benefit. ]