From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B7F2035D615 for ; Fri, 24 Apr 2026 08:52:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777020733; cv=none; b=tvSjZ+1mfPmWUG0Lp0SYX/zTl/tV3wAqt/zUYFcBf70iox3aQOvzjY1khNL/WDoVUQJO/h1pnqiQeNGa6l58AI+PT6CpNiRcoM8asCuNv7WdcQH7ZZbV4PPdoiaCPZ45Schb14UDq/T+63wp+5W5Ui6TMtrx30ox6gVHxzDDMKE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777020733; c=relaxed/simple; bh=qASsn7VxQuNfC4B609WErGpwcV6MK1E6TsPiTPwedI8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cetz7wEaw1HmAExyJroW6cWF1D5vWo4LllHUEZ9fQUehRv7WwMP+PPlzGv1ktAEb72QRCjRQgAJlNPpIRJfj1UT46zOcv33fDeSuxI2d//RnU0qUCkEhNDxgiJ9oR5/uAAgbulD2jibxGesxdZcBeodv/H5WzcgDh/wjF1zrGgs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qHbu6oAS; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="qHbu6oAS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B8724C19425; Fri, 24 Apr 2026 08:52:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777020733; bh=qASsn7VxQuNfC4B609WErGpwcV6MK1E6TsPiTPwedI8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=qHbu6oASLVcSZ08Zpc4nEsoVAmHkOx6JfyjrPg4mtkqF1lLtz1PDsn/tKY0d2CM30 kgm7w96xhaFBSneyNYbU/dEPE0cYQI/OxIpZAi4XBDyQvJwUIDhKT3Fsl2WmNnUO64 8aYT6byMe3dMiAB0jL/9YfxpzgzlI/XBAXczASO/UCSI0j9fxzUN9h3vMVrGdKlwD4 uYPtJ77sKC7Lo8LhDqsuacaHxcVdoOmYWw6rLHkwpiBVH0o7Le7x3BqYMEGfZrEKY/ qIm5aPg9j0h4uuCHaK1rWPEim3c35dnkRrnGkBWVTU60ptfWEYaMVOKlxUYUXYjZ9c 2V7ah/aO9veJg== Message-ID: <1253ca14-69de-418f-8f94-b08e8105e924@kernel.org> Date: Fri, 24 Apr 2026 10:52:06 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/page_alloc: replace kernel_init_pages() with batch page clearing To: "Salunke, Hrushikesh" , Andrew Morton Cc: 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, 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> <20260423041249.156eb95889696ccfaf23dca1@linux-foundation.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/24/26 10:42, Salunke, Hrushikesh wrote: > > On 23-04-2026 16:42, Andrew Morton wrote: >> Caution: This message originated from an External Source. 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. Right. Looking at init_vmalloc_pages(), I wonder if it could also benefit from batching if we find that pages are actually contiguous. That would require looking up multiple pages at once. vmalloc_to_pages() or sth like that. Surely, doing such an optimized page table walk could be beneficial by itself. > > 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. What is exactly is responsible for the code increase? Two calls in clear_highpages_kasan_tagged()? Surely the compiler would just inline kernel_init_pages() already? So my best guess that the 330 bytes are just clear_pages() overhead or some code layout changes? -- Cheers, David