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 bdVFpA52 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 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: List-Subscribe: List-Unsubscribe: Zi Yan writes: > On 13 Apr 2025, at 23:46, Ankur Arora wrote: > >> This series adds multi-page clearing for hugepages. It is a rework >> of [1] which took a detour through PREEMPT_LAZY [2]. >> >> Why multi-page clearing?: multi-page clearing improves upon the >> current page-at-a-time approach by providing the processor with a >> hint as to the real region size. A processor could use this hint to, >> for instance, elide cacheline allocation when clearing a large >> region. >> >> This optimization in particular is done by REP; STOS on AMD Zen >> where regions larger than L3-size use non-temporal stores. >> >> This results in significantly better performance. > > Do you have init_on_alloc=1 in your kernel? > With that, pages coming from buddy allocator are zeroed > in post_alloc_hook() by kernel_init_pages(), which is a for loop > of clear_highpage_kasan_tagged(), a wrap of clear_page(). > And folio_zero_user() is not used. > > At least Debian, Fedora, and Ubuntu by default have > CONFIG_INIT_ON_ALLOC_DEFAULT_ON=y, which means init_on_alloc=1. > > Maybe kernel_init_pages() should get your optimization as well, > unless you only target hugetlb pages. Thanks for the suggestion. I do plan to look for other places where we could be zeroing contiguous regions. Often the problem is that even if the underlying region is contiguous, it isn't so under CONFIG_HIGHMEM. For instance, clear_highpage_kasan_tagged() does a kmap/kunmap_local_page() around the clearing. This breaks the contiguous region into multiple 4K pages even when CONFIG_HIGHMEM is not defined. I wonder if we need a clear_highpages() kind of abstraction which lets HIGHMEM and non-HIGHMEM go their separate ways. -- ankur