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(p200300cbc704a10095ad632501316b1d.dip0.t-ipconnect.de. [2003:cb:c704:a100:95ad:6325:131:6b1d]) by smtp.gmail.com with ESMTPSA id o24-20020a5d58d8000000b002c7066a6f77sm4586083wrf.31.2023.02.22.07.48.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 22 Feb 2023 07:48:57 -0800 (PST) Message-ID: <28a7208c-939c-19ea-1cf0-298444dffe85@redhat.com> Date: Wed, 22 Feb 2023 16:48:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.2 Subject: Re: [PATCH v2 00/46] hugetlb: introduce HugeTLB high-granularity mapping Content-Language: en-US To: Mike Kravetz , James Houghton Cc: Muchun Song , Peter Xu , Andrew Morton , David Rientjes , Axel Rasmussen , Mina Almasry , Zach O'Keefe , Manish Mishra , Naoya Horiguchi , "Dr . David Alan Gilbert" , "Matthew Wilcox (Oracle)" , Vlastimil Babka , Baolin Wang , Miaohe Lin , Yang Shi , Frank van der Linden , Jiaqi Yan , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20230218002819.1486479-1-jthoughton@google.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: 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 21.02.23 22:46, Mike Kravetz wrote: > On 02/18/23 00:27, James Houghton wrote: >> This series introduces the concept of HugeTLB high-granularity mapping >> (HGM). This series teaches HugeTLB how to map HugeTLB pages at >> high-granularity, similar to how THPs can be PTE-mapped. >> >> Support for HGM in this series is for MAP_SHARED VMAs on x86_64 only. Other >> architectures and (some) support for MAP_PRIVATE will come later. >> >> This series is based on latest mm-unstable (ccd6a73daba9). >> >> Notable changes with this series >> ================================ >> >> - hugetlb_add_file_rmap / hugetlb_remove_rmap are added to handle >> mapcounting for non-anon hugetlb. >> - The mapcounting scheme uses subpages' mapcounts for high-granularity >> mappings, but it does not use subpages_mapcount(). This scheme >> prevents the HugeTLB VMEMMAP optimization from being used, so it >> will be improved in a later series. >> - page_add_file_rmap and page_remove_rmap are updated so they can be >> used by hugetlb_add_file_rmap / hugetlb_remove_rmap. >> - MADV_SPLIT has been added to enable the userspace API changes that >> HGM allows for: high-granularity UFFDIO_CONTINUE (and maybe other >> changes in the future). MADV_SPLIT does NOT force all the mappings to >> be PAGE_SIZE. >> - MADV_COLLAPSE is expanded to include HugeTLB mappings. >> >> Old versions: >> v1: https://lore.kernel.org/linux-mm/20230105101844.1893104-1-jthoughton@google.com/ >> RFC v2: https://lore.kernel.org/linux-mm/20221021163703.3218176-1-jthoughton@google.com/ >> RFC v1: https://lore.kernel.org/linux-mm/20220624173656.2033256-1-jthoughton@google.com/ >> >> Changelog: >> v1 -> v2 (thanks Peter for all your suggestions!): >> - Changed mapcount to be more THP-like, and make HGM incompatible with >> HVO. >> - HGM is now disabled by default to leave HVO enabled by default. > > I understand the reasoning behind the move to THP-like mapcounting, and the > incompatibility with HVO. However, I just got to patch 5 and realized either > HGM or HVO will need to be chosen at kernel build time. That may not be an > issue for cloud providers or others building their own kernels for internal > use. However, distro kernels will need to pick one option or the other. > Right now, my Fedora desktop has HVO enabled so it would likely not have > HGM enabled. That is not a big deal for a desktop. > > Just curious, do we have distro kernel users that want to use HGM? Most certainly I would say :) -- Thanks, David / dhildenb