[{"id":3673567,"web_url":"http://patchwork.ozlabs.org/comment/3673567/","msgid":"","date":"2026-04-05T13:34:53","subject":"Re: [PATCH 00/49] mm: Generalize vmemmap optimization for DAX and\n HugeTLB","submitter":{"id":77733,"url":"http://patchwork.ozlabs.org/api/people/77733/","name":"Mike Rapoport","email":"rppt@kernel.org"},"content":"Hi Muchun,\n\nOn Sun, Apr 05, 2026 at 08:51:51PM +0800, Muchun Song wrote:\n> Overview:\n> This patch series generalizes the HugeTLB Vmemmap Optimization (HVO)\n> into a generic vmemmap optimization framework that can be used by both\n> HugeTLB and DAX.\n> \n> Background:\n> Currently, the vmemmap optimization feature is highly coupled with\n> HugeTLB. However, DAX also has similar requirements for optimizing vmemmap\n> pages to save memory. The current implementation has separate vmemmap\n> optimization paths for HugeTLB and DAX, leading to duplicated logic,\n> complex initialization sequences, and architecture-specific flags.\n> \n> Implementation:\n> This series breaks down the optimization into a generic framework:\n> - Patch 1-6: Fix bugs related to sparse vmemmap initialization and DAX.\n> - Patch 7-13: Refactor the existing sparse vmemmap initialization.\n> - Patch 14-26: Decouple the vmemmap optimization from HugeTLB and\n> introduce generic optimization macros and functions.\n> - Patch 27-39: Switch HugeTLB and DAX to use the generic framework.\n> - Patch 40-49: Clean up the old HVO-specific code and simplify it.\n> \n> Benifit:\n> - When CONFIG_DEFERRED_STRUCT_PAGE_INIT is disabled, all struct pages\n> utilizing HVO (HugeTLB Vmemmap Optimization) skip initialization in\n> memmap_init, significantly accelerating boot times.\n> - All architectures supporting HVO benefit from the optimizations \n> provided by SPARSEMEM_VMEMMAP_PREINIT without requiring \n> architecture-specific adaptations.\n> - Device DAX struct page savings are further improved, saving an \n> additional 4KB of struct page memory for every 2MB huge page.\n> - Vmemmap tail pages used for Device DAX shared mappings are changed \n> from read-write to read-only, enhancing system security.\n> - HugeTLB and Device DAX now share a unified vmemmap optimization \n> framework, reducing long-term maintenance overhead.\n\nThis looks very interesting ...\n \n> 32 files changed, 513 insertions(+), 1197 deletions(-)\n\n... and nicely cleaning up things.\n\nThis series is high on my TODO list, but most likely I won't have time for\nproper review until after -rc1.","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256\n header.s=k20201202 header.b=JsuR22bB;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=112.213.38.117; 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Howlett\" ,\n\tVlastimil Babka ,\n\tSuren Baghdasaryan ,\n\tMichal Hocko , Nicholas Piggin ,\n\tChristophe Leroy , aneesh.kumar@linux.ibm.com,\n\tjoao.m.martins@oracle.com, linux-mm@kvack.org,\n\tlinuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org","Subject":"Re: [PATCH 00/49] mm: Generalize vmemmap optimization for DAX and\n HugeTLB","Message-ID":"","References":"<20260405125240.2558577-1-songmuchun@bytedance.com>","X-Mailing-List":"linuxppc-dev@lists.ozlabs.org","List-Id":"","List-Help":"","List-Owner":"","List-Post":"","List-Archive":",\n ","List-Subscribe":",\n ,\n ","List-Unsubscribe":"","Precedence":"list","MIME-Version":"1.0","Content-Type":"text/plain; charset=us-ascii","Content-Disposition":"inline","In-Reply-To":"<20260405125240.2558577-1-songmuchun@bytedance.com>","X-Spam-Status":"No, score=-0.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED,\n\tDKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS\n\tautolearn=disabled version=4.0.1 OzLabs 8","X-Spam-Checker-Version":"SpamAssassin 4.0.1 (2024-03-25) on lists.ozlabs.org"}}]