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Fri, 24 Apr 2026 03:42:03 -0500 Message-ID: Date: Fri, 24 Apr 2026 14:12:02 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/page_alloc: replace kernel_init_pages() with batch page clearing To: Andrew Morton CC: , , , , , , , , , , , , , , , , References: <20260422102729.166599-1-hsalunke@amd.com> <20260423041249.156eb95889696ccfaf23dca1@linux-foundation.org> Content-Language: en-US From: "Salunke, Hrushikesh" In-Reply-To: <20260423041249.156eb95889696ccfaf23dca1@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Received-SPF: None (SATLEXMB03.amd.com: hsalunke@amd.com does not designate permitted sender hosts) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL02EPF0002992D:EE_|CH1PR12MB9647:EE_ X-MS-Office365-Filtering-Correlation-Id: fb683f92-43e7-4ac8-0a1a-08dea1dd5eb3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700016|1800799024|82310400026|7416014|376014|18002099003|22082099003|56012099003; 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Use proper caution when opening attachments, clicking links, or responding. > > > On Wed, 22 Apr 2026 10:26:58 +0000 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. >> >> Replace kernel_init_pages() with direct calls to the new helper, as it >> becomes a trivial wrapper. >> >> Allocating 8192 x 2MB HugeTLB pages (16GB) with init_on_alloc=1: >> >> Before: 0.445s >> After: 0.166s (-62.7%, 2.68x faster) > Nice. > >> 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% >> >> ... >> >> --- a/include/linux/highmem.h >> +++ b/include/linux/highmem.h >> @@ -345,6 +345,21 @@ 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) >> +{ >> + /* s390's use of memset() could override KASAN redzones. */ >> + kasan_disable_current(); >> + if (!IS_ENABLED(CONFIG_HIGHMEM)) { >> + clear_pages(kasan_reset_tag(page_address(page)), numpages); >> + } else { >> + int i; >> + >> + for (i = 0; i < numpages; i++) >> + clear_highpage_kasan_tagged(page + i); >> + } >> + kasan_enable_current(); >> +} > Why was it globally published and inlined? Is there any expectation > that this will be used outside of page_alloc.c? > > Both of the callsites are themselves inlined. The patch adds 330 bytes > to my arm allmodcnfig page_alloc.o - did we gain anything from that? > Hi Andrew, The idea was to keep it alongside clear_highpage_kasan_tagged() as its batch counterpart, but currently it is only used by page_alloc.c. Your concern about the code size increase is valid. Would you prefer if I move it to page_alloc.c as a static function and drop the inline in v4? If an external user comes along later it can always be moved back to the header. regards, Hrushikesh