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t=1776882355; bh=xiGG7jgIF7pLqLmsu6Dker8kDFGD8xhSO9MbaoWa4Qc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=e/+NyOPvnKLr2hmkxcEGLNU2AwVc8jV0jl2N4Y46EsujQ+RIyuK6tNdYh3/T0rfyi 7FT8eo6BT3t0ej/WKd44pEToKZcGwEfvOs/x1Nyt86vjWYLnbNBrS8LPxjiUG/Fe0d 6F0HGTCMdJzbq9xjP/2hh5qNkxxbbaSiYwtlmaUc2sxJFBDNPDds8D7p9dFdSzdLiC ilYeBoSaSxmLbx+8OrwNt+lDiRC9W02dc/yaocFn85e6zD/gDbp5X1sakqLckC2wVf QgvWgZbJPrEN9E4ifdUyySZ4nfHEpNiRCMFxGj4Zi9ln+GE+9MOFhXQTsEZ05z+6Kw 3AjCdTwQBF13g== Message-ID: Date: Wed, 22 Apr 2026 20:25:48 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/page_alloc: replace kernel_init_pages() with batch page clearing To: Hrushikesh Salunke , akpm@linux-foundation.org, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, rkodsara@amd.com, bharata@amd.com, ankur.a.arora@oracle.com, shivankg@amd.com References: <20260422102729.166599-1-hsalunke@amd.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: A4E83C000D X-Stat-Signature: czi9dg6f1iufr3tuyryiaqhzjeu4kjxc X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1776882356-942460 X-HE-Meta: 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 dGwLd7+c aNuhRYGN+K6Tg4GSGhGZSIQpEdGmAuGUfL7Odz+Dt/wnDBUfnijy0qKsw1lTZre0MexAVdtj3TghSuoVkBVxgRNqiCYfwUq+t+oE7XJiku8syBCp3GprfIfipYzsM+X2/3tAE9cJTBkIBtXg6YuM9cJaulk/KEOoAeAjn+mmygSp737vc9XXOkC6+AcdApXCyFivMmUL8SeVmcF5dR3kWPj0EmYSF1OXPhmiQDTW4ci+GesPUPL//waav4dE14qGbHndeaSIe7j8L1qSo/omBzKleveIeW+PA4HclTjkLMr159wYkQ93gzvouW/m9nRJA7aBEMaJi4A2OEUA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/22/26 12:26, 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) > > 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% We do have some elaborate handling in clear_contig_highpages() to chunk it up (and to call cond_resched()). But that function can get called with much bigger ranges. I'm not concerned about the cond_resched() -- we wouldn't do one here before -- but I'm wondering whether we could end up triggering a HW instruction that is uninterruptible and takes a rather long time. But clear_contig_highpages() breaks it into 32MiB chunks, and only x86 supports it so far. So we won't exceed that with the maximum buddy order of 4MiB on x86. Acked-by: David Hildenbrand (Arm) -- Cheers, David