Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1176048AbdDYJOK (ORCPT ); Tue, 25 Apr 2017 05:14:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52648 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1177210AbdDYJNK (ORCPT ); Tue, 25 Apr 2017 05:13:10 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 486F67F4C7 Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=xlpang@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 486F67F4C7 From: Xunlei Pang To: linux-kernel@vger.kernel.org, kexec@lists.infradead.org Cc: akpm@linux-foundation.org, Eric Biederman , Dave Young , x86@kernel.org, Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , Yinghai Lu , Xunlei Pang Subject: [PATCH 2/2] x86_64/kexec: Use PUD level 1GB page for identity mapping if available Date: Tue, 25 Apr 2017 17:13:02 +0800 Message-Id: <1493111582-28261-2-git-send-email-xlpang@redhat.com> In-Reply-To: <1493111582-28261-1-git-send-email-xlpang@redhat.com> References: <1493111582-28261-1-git-send-email-xlpang@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Tue, 25 Apr 2017 09:13:10 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1698 Lines: 44 Kexec setups all identity mappings before booting into the new kernel, and this will cause extra memory consumption for paging structures which is quite considerable on modern machines with huge memory. E.g. On one 32TB machine, in kdump case, it could waste around 128MB (around 4MB/TB) from the reserved memory after kexec set all the identity mappings using the current 2MB page, plus the loaded kdump kernel, initramfs, etc, it caused kexec syscall -NOMEM failure. As a result, we had to enlarge reserved memory via "crashkernel=X". This causes some trouble for distributions that use policies to evaluate the proper "crashkernel=X" value for users. Given that on machines with large number of memory, 1GB feature is very likely available, and that kernel_ident_mapping_init() supports PUD level 1GB page, to solve this problem, we use 1GB size page to create the identity mapping pgtable for kdump if 1GB feature is available. Signed-off-by: Xunlei Pang --- arch/x86/kernel/machine_kexec_64.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c index 1d4f2b0..41f1ae7 100644 --- a/arch/x86/kernel/machine_kexec_64.c +++ b/arch/x86/kernel/machine_kexec_64.c @@ -122,6 +122,11 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable) level4p = (pgd_t *)__va(start_pgtable); clear_page(level4p); + + /* Use PUD level page if available, to save crash memory for kdump */ + if (direct_gbpages) + info.use_pud_page = true; + for (i = 0; i < nr_pfn_mapped; i++) { mstart = pfn_mapped[i].start << PAGE_SHIFT; mend = pfn_mapped[i].end << PAGE_SHIFT; -- 1.8.3.1