From patchwork Fri Apr 4 15:59:53 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: David Woodhouse X-Patchwork-Id: 14038666 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A3E88C36010 for ; Fri, 4 Apr 2025 16:08:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:Message-ID:Date:Subject:Cc:To:From:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:List-Owner; bh=P5VYLYdEkeWgyeWX/EZa0WnpJ73Q8FAesiLU/ww7Cxs=; b=ninKwQvR3ZR3OirlzHvFjp0Tbs DLZtT9NoUND89ZsWPDjfaCuWK2xMsgCXUEvIVui7Bmvmpb2BnuN1WlJjUFafIzku/Gw8NI9q7jSGq airbHBL0U5mrpgK0huA1RGhn9BVcqVbqfbm8qRrUfRqypcT2nHwngLx8E/ZEAqeja1lrz1JNb2PFD g36kFxZbWiuEXxmBbIAoFIGxBNfdoq98Eufq8iMHc1vWOF2LmpctvOFnC/DKK9V48I34E0zZn0HZF iUn4im99yMnrLG+TRdMPkGGfCAxS93m8zkU1SFlN0YwF1X7z9ntNIqajHhMu6bj2Le6EshNZHdT3H QBudefuw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.1 #2 (Red Hat Linux)) id 1u0jad-0000000CGFr-3SYx; Fri, 04 Apr 2025 16:08:19 +0000 Received: from desiato.infradead.org ([2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by bombadil.infradead.org with esmtps (Exim 4.98.1 #2 (Red Hat Linux)) id 1u0jSf-0000000CF3d-2SZX for linux-arm-kernel@bombadil.infradead.org; Fri, 04 Apr 2025 16:00:05 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding: Content-Type:MIME-Version:Message-ID:Date:Subject:Cc:To:From:Reply-To: Content-ID:Content-Description:In-Reply-To:References; bh=P5VYLYdEkeWgyeWX/EZa0WnpJ73Q8FAesiLU/ww7Cxs=; b=GUYU/YR47lcF88YQE7EH7TpKB2 zN7AKKvvGE+bbZSCVfqr/oyxCsvOKug18HG2HLPn2hzCCyr28tFqyGD9WE8XnLgGAI3tZkFoNGjRO OgjbHNJH1PDByFVu8pm8ZivdCL5MEV/GNaFUfd+wAfiibiI9zWlpJtBcaljmCVRXvO2F5RxGRDFcv n+kIPUAtdP9Y82yL00kM9ObdiypoF5byTbPDzb62xDr08XwYD5r8jUm8sLxrmkORJzVZ3UuKodDTs Em+8VmA6k36CwWivAtW5UVU9ugF9e40TqXDlsMyj8sHumr6FwIMVgjq+YOd/BBlhaaZ+R0N+DDoUj 9yqvaGVQ==; Received: from [2001:8b0:10b:1::ebe] (helo=i7.infradead.org) by desiato.infradead.org with esmtpsa (Exim 4.98.1 #2 (Red Hat Linux)) id 1u0jSc-00000007QOy-0YLc; Fri, 04 Apr 2025 16:00:02 +0000 Received: from dwoodhou by i7.infradead.org with local (Exim 4.98.1 #2 (Red Hat Linux)) id 1u0jSZ-0000000ERSB-2cgL; Fri, 04 Apr 2025 16:59:59 +0100 From: David Woodhouse To: Mike Rapoport Cc: Andrew Morton , "Sauerwein, David" , Anshuman Khandual , Ard Biesheuvel , Catalin Marinas , David Hildenbrand , Marc Zyngier , Mark Rutland , Mike Rapoport , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH v2 1/7] mm: Introduce for_each_valid_pfn() and use it from reserve_bootmem_region() Date: Fri, 4 Apr 2025 16:59:53 +0100 Message-ID: <20250404155959.3442111-1-dwmw2@infradead.org> X-Mailer: git-send-email 2.49.0 MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: David Woodhouse Especially since commit 9092d4f7a1f8 ("memblock: update initialization of reserved pages"), the reserve_bootmem_region() function can spend a significant amount of time iterating over every 4KiB PFN in a range, calling pfn_valid() on each one, and ultimately doing absolutely nothing. On a platform used for virtualization, with large NOMAP regions that eventually get used for guest RAM, this leads to a significant increase in steal time experienced during kexec for a live update. Introduce for_each_valid_pfn() and use it from reserve_bootmem_region(). This implementation is precisely the same naïve loop that the function used to have, but subsequent commits will provide optimised versions for FLATMEM and SPARSEMEM, and this version will remain for those architectures which provide their own pfn_valid() implementation, until/unless they also provide a matching for_each_valid_pfn(). Signed-off-by: David Woodhouse Reviewed-by: Mike Rapoport (Microsoft) --- include/linux/mmzone.h | 10 ++++++++++ mm/mm_init.c | 23 ++++++++++------------- 2 files changed, 20 insertions(+), 13 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 25e80b2ca7f4..32ecb5cadbaf 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -2176,6 +2176,16 @@ void sparse_init(void); #define subsection_map_init(_pfn, _nr_pages) do {} while (0) #endif /* CONFIG_SPARSEMEM */ +/* + * Fallback case for when the architecture provides its own pfn_valid() but + * not a corresponding for_each_valid_pfn(). + */ +#ifndef for_each_valid_pfn +#define for_each_valid_pfn(_pfn, _start_pfn, _end_pfn) \ + for ((_pfn) = (_start_pfn); (_pfn) < (_end_pfn); (_pfn)++) \ + if (pfn_valid(_pfn)) +#endif + #endif /* !__GENERATING_BOUNDS.H */ #endif /* !__ASSEMBLY__ */ #endif /* _LINUX_MMZONE_H */ diff --git a/mm/mm_init.c b/mm/mm_init.c index a38a1909b407..7c699bad42ad 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -777,22 +777,19 @@ static inline void init_deferred_page(unsigned long pfn, int nid) void __meminit reserve_bootmem_region(phys_addr_t start, phys_addr_t end, int nid) { - unsigned long start_pfn = PFN_DOWN(start); - unsigned long end_pfn = PFN_UP(end); + unsigned long pfn; - for (; start_pfn < end_pfn; start_pfn++) { - if (pfn_valid(start_pfn)) { - struct page *page = pfn_to_page(start_pfn); + for_each_valid_pfn (pfn, PFN_DOWN(start), PFN_UP(end)) { + struct page *page = pfn_to_page(pfn); - init_deferred_page(start_pfn, nid); + init_deferred_page(pfn, nid); - /* - * no need for atomic set_bit because the struct - * page is not visible yet so nobody should - * access it yet. - */ - __SetPageReserved(page); - } + /* + * no need for atomic set_bit because the struct + * page is not visible yet so nobody should + * access it yet. + */ + __SetPageReserved(page); } }