Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758018AbcLOQH3 (ORCPT ); Thu, 15 Dec 2016 11:07:29 -0500 Received: from mail-it0-f48.google.com ([209.85.214.48]:35178 "EHLO mail-it0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757439AbcLOQH2 (ORCPT ); Thu, 15 Dec 2016 11:07:28 -0500 MIME-Version: 1.0 In-Reply-To: <20161215153930.GA8111@rric.localdomain> References: <1481706707-6211-1-git-send-email-ard.biesheuvel@linaro.org> <1481706707-6211-3-git-send-email-ard.biesheuvel@linaro.org> <20161215153930.GA8111@rric.localdomain> From: Ard Biesheuvel Date: Thu, 15 Dec 2016 16:07:26 +0000 Message-ID: Subject: Re: [PATCH 2/2] arm64: mm: enable CONFIG_HOLES_IN_ZONE for NUMA To: Robert Richter Cc: "linux-arm-kernel@lists.infradead.org" , Will Deacon , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Catalin Marinas , Andrew Morton , Hanjun Guo , Yisheng Xie , James Morse Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1350 Lines: 34 On 15 December 2016 at 15:39, Robert Richter wrote: > I was going to do some measurements but my kernel crashes now with a > page fault in efi_rtc_probe(): > > [ 21.663393] Unable to handle kernel paging request at virtual address 20251000 > [ 21.663396] pgd = ffff000009090000 > [ 21.663401] [20251000] *pgd=0000010ffff90003 > [ 21.663402] , *pud=0000010ffff90003 > [ 21.663404] , *pmd=0000000fdc030003 > [ 21.663405] , *pte=00e8832000250707 > > The sparsemem config requires the whole section to be initialized. > Your patches do not address this. > 96000047 is a third level translation fault, and the PTE address has RES0 bits set. I don't see how this is related to sparsemem, could you explain? > On 14.12.16 09:11:47, Ard Biesheuvel wrote: >> +config HOLES_IN_ZONE >> + def_bool y >> + depends on NUMA > > This enables pfn_valid_within() for arm64 and causes the check for > each page of a section. The arm64 implementation of pfn_valid() is > already expensive (traversing memblock areas). Now, this is increased > by a factor of 2^18 for 4k page size (16384 for 64k). We need to > initialize the whole section to avoid that. > I know that. But if you want something for -stable, we should have something that is correct first, and only then care about the performance hit (if there is one)