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RHuUr3pXEsi0et4F0r7jSHQuGhk5L1jDbIsEDtICZG6qBGaBwjSXz/p5sSh8MhyxEwjdR2aW99EZevZfnEDsa9NtOz27bNlLgUu96VOmY+c++qJeyikwNlA8bKgUoGInEiqbBIDaoibhstdrFfWYaYTxytVffBRd3fwmVx+SSjFJE6sSfCVnqq4mmUHW3WC3nznHVBVmjzoozZGehDjXs+aW/ARoES/3pIWmqThAubjbPiwdAWoggMVLt1FiywG71jR5iGgnUxQPo1JmfJv1AjhfNLzUppZw8uCFA7UWOOn0pMK3yC6sp7c301JpaQpXqVCN1nbgw7k2mJFHGkLe+wsjpLZ4lQ7P3ySx3QunLDNzs4STK/q48u68lDOtkFBRYrlUTNnK1RiTkl3TPI6cPi6MYvGcoAXE8Mz+Bxn8a+6yMYnO6ML7b85YzUfNxk+OHC8tx Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 21 Apr 2026, at 0:24, Hrushikesh Salunke wrote: > When init_on_alloc is enabled, kernel_init_pages() clears every page > one at a time via clear_highpage_kasan_tagged(), which incurs per-page > kmap_local_page()/kunmap_local() overhead and prevents the architecture > clearing primitive from operating on contiguous ranges. > > Introduce clear_highpages_kasan_tagged() in highmem.h, a batch > clearing helper that calls clear_pages() for the full contiguous range > on !HIGHMEM systems, bypassing the per-page kmap overhead and allowing > a single invocation of the arch clearing primitive across the entire > allocation. The HIGHMEM path falls back to per-page clearing since > those pages require kmap. > > Use it in kernel_init_pages() to replace the per-page loop. > > Allocating 8192 x 2MB HugeTLB pages (16GB) with init_on_alloc=1: > > Before: 0.445s > After: 0.166s (-62.7%, 2.68x faster) > > Kernel time (sys) reduction per workload with init_on_alloc=1: > > Workload Before After Change > Graph500 64C128T 30m 41.8s 15m 14.8s -50.3% > Graph500 16C32T 15m 56.7s 9m 43.7s -39.0% > Pagerank 32T 1m 58.5s 1m 12.8s -38.5% > Pagerank 128T 2m 36.3s 1m 40.4s -35.7% > > Signed-off-by: Hrushikesh Salunke > --- > base commit: f1541b40cd422d7e22273be9b7e9edfc9ea4f0d7 > > v1: https://lore.kernel.org/all/20260408092441.435133-1-hsalunke@amd.com/ > > Changes since v1: > - Dropped cond_resched() and PROCESS_PAGES_NON_PREEMPT_BATCH as > kernel_init_pages() runs inside the page allocator and can be > called from atomic context, making cond_resched() unsafe. The > original code never had a cond_resched() here, and the > performance gain comes from batching, not rescheduling. > > - Moved the !HIGHMEM/HIGHMEM branching into a new > clear_highpages_kasan_tagged() helper in highmem.h, per David's > suggestion. > > include/linux/highmem.h | 12 ++++++++++++ > mm/page_alloc.c | 5 +---- > 2 files changed, 13 insertions(+), 4 deletions(-) > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > index af03db851a1d..ad0f42d06ce6 100644 > --- a/include/linux/highmem.h > +++ b/include/linux/highmem.h > @@ -345,6 +345,18 @@ static inline void clear_highpage_kasan_tagged(struct page *page) > kunmap_local(kaddr); > } > > +static inline void clear_highpages_kasan_tagged(struct page *page, int numpages) > +{ > + if (!IS_ENABLED(CONFIG_HIGHMEM)) { > + clear_pages(kasan_reset_tag(page_address(page)), numpages); kasan_reset_tag() here removes the tag from page address, so that clear_pages() can use the right kaddr. I thought each page needs a kasan_reset_tag(). No need to respond here, as I am reading the code and trying to understand how it works. Acked-by: Zi Yan > + } else { > + int i; > + > + for (i = 0; i < numpages; i++) > + clear_highpage_kasan_tagged(page + i); > + } > +} > + > #ifndef __HAVE_ARCH_TAG_CLEAR_HIGHPAGES > > /* Return false to let people know we did not initialize the pages */ > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index b1c5430cad4e..1aaf7f839ff4 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1220,12 +1220,9 @@ static inline bool should_skip_kasan_poison(struct page *page) > > static void kernel_init_pages(struct page *page, int numpages) > { > - int i; > - > /* s390's use of memset() could override KASAN redzones. */ > kasan_disable_current(); > - for (i = 0; i < numpages; i++) > - clear_highpage_kasan_tagged(page + i); > + clear_highpages_kasan_tagged(page, numpages); > kasan_enable_current(); > } > > -- > 2.43.0 Best Regards, Yan, Zi