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a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=Wb1JkmetP80A:10 a=GoEa3M9JfhUA:10 a=VwQbUJbxAAAA:8 a=Ikd4Dj_1AAAA:8 a=20KFwNOVAAAA:8 a=yPCof4ZbAAAA:8 a=5gTFVFuSgBvqhr89u34A:9 X-Proofpoint-ORIG-GUID: qnx7t0VFibwnQWxRHvBUuUXzzDJWs5b6 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzE0MDEzNiBTYWx0ZWRfX4lJlale9yrF/ N2ZHMxilP4Kf9eX+SNxsIhMkGDxrDX7SKK5X0LAfn1C5BTepibOEdI6XceOQeen/JhW9MiG0cZr NRmKtgyQVrApqt3qSsKH8PeB3m8h61y6bzqUbhsjZbfdDItZCuHHQs36AJqx5SBcBVuvRdgShWe gtriZ9iyAjkZpRM7VLHPm05jgLjMhlDOHx9ETBQTrZEwUvIuoYI2umUXLocwid4s7kWtaCrrlos fU8dlggnr/V04BG5a1cAE4BJer2jM0YXOGmmBZ+L/fm/s8s437FGwUOuhI4+Arugyt+YqzoBD1g 5ZE5ZmmySJgs4i26FAgn6J+UWnJsi2k4yAbxRgPtcjwDYqin6lnzJwNrKt1ox54swo+w6K2MkI0 eV7tuOS2lVpGGkQKjnqgNvSk0aPgTMdZowtIa85zaXRMdMRAb1KdBWkwxrmIq7T3yHH/o5oF X-Proofpoint-GUID: qnx7t0VFibwnQWxRHvBUuUXzzDJWs5b6 [ Added Zi Yan. ] David Hildenbrand writes: > On 11.07.25 19:32, Ankur Arora wrote: >> David Hildenbrand writes: >> >>> On 10.07.25 02:59, Ankur Arora wrote: >>>> Add CONFIG_CLEAR_PAGE_EXTENT to allow clearing of page-extents >>>> where architecturally supported. >>>> This is only available with !CONFIG_HIGHMEM because the intent is to >>>> use architecture support to clear contiguous extents in a single >>>> operation (ex. via FEAT_MOPS on arm64, string instructions on x86) >>>> which excludes any possibility of interspersing kmap()/kunmap(). >>>> Signed-off-by: Ankur Arora >>>> --- >>> >>> Staring at the next patch, I think this can easily be squashed into the next >>> patch where you add actual MM core support. >> I wanted to do this in a separate patch to explicitly document what the >> responsibility of the interface provided by the architecture is. >> That said, the commit message didn't actually do a good job of doing >> that :D. >> Copying the more detailed commit message from my reply to Andrew, >> one important part of the clear_pages() is that it be interruptible >> because clear_pages_resched() implicitly depends on it. >> >>> This is only enabled with !CONFIG_HIGHMEM because the intent is >>> to use architecture support to clear contiguous extents in a >>> single interruptible operation (ex. via FEAT_MOPS on arm64, >>> string instructions on x86). >> >>> Given that we might be zeroing the whole extent with a single >>> instruction, this excludes any possibility of constructing >>> intermediate HIGHMEM maps. >> Do you think it is best documented in the next patch in a comment >> instead? > > I would just add + document it as part of the next patch. > > Looking at the bigger picture now, you introduce > > ARCH_HAS_CLEAR_PAGES > > To say whether an architecture provides clear_pages(). > > Now we want to conditionally use that to optimize folio_zero_user(). > > Remind me, why do we want to glue this to THP / HUGETLBFS only? I would assume > that the code footprint is rather small, and the systems out there that are > compiled with ARCH_HAS_CLEAR_PAGES but without THP / HUGETLBFS are rather ... > rare (mostly 32BIT x86 only). I thought about this some more and there are a few other interfaces that end up clearing pages: > clear_highpage() > clear_highpage_kasan_tagged() > tag_clear_highpage() In this set, there are many loops of the form: for (i = 0; i < n; i++) clear_highpage(); At least some of these (including kernel_init_pages()) could be migrated to variations on a clear_highpages() which could be: static inline void clear_highpages(struct page *page, u32 num_pages) { if (!IS_ENABLED(CONFIG_HIGHMEM)) clear_pages_resched(page, num_pages); else for (i = 0; i < num_pages; ++i) clear_highpage(page + i); } (clear_pages_resched() should be safe to be used from here because everybody using this should be in a schedulable context.) (The kernel_init_pages() was also suggested by Zi Yan in a review of v3 [1].) > clear_user_highpage() Only users folio_zero_user(), __collapse_huge_page_copy() and userfaultd. > clear_user_page() Not many users apart from the highmem interface. > clear_page() Not many users apart from the highmem interface. I'm happy to do this work, just not sure how to stage it. In particular I would like to avoid a series which tries to address all of the cases. Maybe it makes sense to handle just add the clear_highpages() variants, folio_zero_user() handling and some of the obvious users of clear_highpages() for v6? Thanks Ankur [1] https://lore.kernel.org/lkml/AC2C5344-E655-45BB-B90B-D63C4AC8F2F6@nvidia.com/