From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8B74EC3279B for ; Fri, 6 Jul 2018 22:37:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3B65422B1C for ; Fri, 6 Jul 2018 22:37:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3B65422B1C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754296AbeGFWhN (ORCPT ); Fri, 6 Jul 2018 18:37:13 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36516 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753993AbeGFWhL (ORCPT ); Fri, 6 Jul 2018 18:37:11 -0400 Received: from akpm3.svl.corp.google.com (unknown [104.133.9.92]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 971ABDA5; Fri, 6 Jul 2018 22:37:10 +0000 (UTC) Date: Fri, 6 Jul 2018 15:37:09 -0700 From: Andrew Morton To: Jia He Cc: Russell King , Catalin Marinas , Will Deacon , Mark Rutland , Ard Biesheuvel , Michal Hocko , Wei Yang , Kees Cook , Laura Abbott , Vladimir Murzin , Philip Derrin , AKASHI Takahiro , James Morse , Steve Capper , Pavel Tatashin , Gioh Kim , Vlastimil Babka , Mel Gorman , Johannes Weiner , Kemi Wang , Petr Tesarik , YASUAKI ISHIMATSU , Andrey Ryabinin , Nikolay Borisov , Daniel Jordan , Daniel Vacek , Eugeniu Rosca , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Jia He Subject: Re: [RESEND PATCH v10 2/6] mm: page_alloc: remain memblock_next_valid_pfn() on arm/arm64 Message-Id: <20180706153709.6bcc76b0245f239f1d1dcc8a@linux-foundation.org> In-Reply-To: <1530867675-9018-3-git-send-email-hejianet@gmail.com> References: <1530867675-9018-1-git-send-email-hejianet@gmail.com> <1530867675-9018-3-git-send-email-hejianet@gmail.com> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 6 Jul 2018 17:01:11 +0800 Jia He wrote: > From: Jia He > > Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns > where possible") optimized the loop in memmap_init_zone(). But it causes > possible panic bug. So Daniel Vacek reverted it later. > > But as suggested by Daniel Vacek, it is fine to using memblock to skip > gaps and finding next valid frame with CONFIG_HAVE_ARCH_PFN_VALID. > Daniel said: > "On arm and arm64, memblock is used by default. But generic version of > pfn_valid() is based on mem sections and memblock_next_valid_pfn() does > not always return the next valid one but skips more resulting in some > valid frames to be skipped (as if they were invalid). And that's why > kernel was eventually crashing on some !arm machines." > > About the performance consideration: > As said by James in b92df1de5, > "I have tested this patch on a virtual model of a Samurai CPU > with a sparse memory map. The kernel boot time drops from 109 to > 62 seconds." > > Thus it would be better if we remain memblock_next_valid_pfn on arm/arm64. > We're making a bit of a mess here. mmzone.h: ... #ifndef CONFIG_HAVE_ARCH_PFN_VALID ... #define next_valid_pfn(pfn) (pfn + 1) #endif ... #ifdef CONFIG_HAVE_MEMBLOCK_PFN_VALID #define next_valid_pfn(pfn) memblock_next_valid_pfn(pfn) ... #else ... #ifndef next_valid_pfn #define next_valid_pfn(pfn) (pfn + 1) #endif I guess it works OK, since CONFIG_HAVE_MEMBLOCK_PFN_VALID depends on CONFIG_HAVE_ARCH_PFN_VALID. But it could all do with some cleanup and modernization. - Perhaps memblock_next_valid_pfn() should just be called pfn_valid(). So the header file's responsibility is to provide pfn_valid() and next_valid_pfn(). - CONFIG_HAVE_ARCH_PFN_VALID should go away. The current way of doing such thnigs is for the arch (or some Kconfig combination) to define pfn_valid() and next_valid_pfn() in some fashion and to then ensure that one of them is #defined to something, to indicate that both of these have been set up. Or something like that. Secondly, in memmap_init_zone() > - if (!early_pfn_valid(pfn)) > + if (!early_pfn_valid(pfn)) { > + pfn = next_valid_pfn(pfn) - 1; > continue; > + } > + This is weird-looking. next_valid_pfn(pfn) is usually (pfn+1) so it's a no-op. Sometimes we're calling memblock_next_valid_pfn() and then backing up one, presumably because the `for' loop ends in `pfn++'. Or something. Can this please be fully commented or cleaned up?