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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 51E03ECE560 for ; Mon, 24 Sep 2018 16:52:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0D6392145D for ; Mon, 24 Sep 2018 16:52:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0D6392145D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.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 S1732796AbeIXWzs (ORCPT ); Mon, 24 Sep 2018 18:55:48 -0400 Received: from mx2.suse.de ([195.135.220.15]:35788 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729808AbeIXWzs (ORCPT ); Mon, 24 Sep 2018 18:55:48 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C12C4AE6B; Mon, 24 Sep 2018 16:52:43 +0000 (UTC) Date: Mon, 24 Sep 2018 18:52:42 +0200 From: Michal Hocko To: Anshuman Khandual Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org Subject: Re: [PATCH] mm/migrate: Split only transparent huge pages when allocation fails Message-ID: <20180924164733.GG18685@dhcp22.suse.cz> References: <1537798495-4996-1-git-send-email-anshuman.khandual@arm.com> <20180924143027.GE18685@dhcp22.suse.cz> <421f9b78-cb0f-01ce-dca0-93ff6eae0816@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <421f9b78-cb0f-01ce-dca0-93ff6eae0816@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 24-09-18 22:10:30, Anshuman Khandual wrote: > > > On 09/24/2018 08:00 PM, Michal Hocko wrote: > > On Mon 24-09-18 19:44:55, Anshuman Khandual wrote: > >> When unmap_and_move[_huge_page] function fails due to lack of memory, the > >> splitting should happen only for transparent huge pages not for HugeTLB > >> pages. PageTransHuge() returns true for both THP and HugeTLB pages. Hence > >> the conditonal check should test PagesHuge() flag to make sure that given > >> pages is not a HugeTLB one. > > > > Well spotted! Have you actually seen this happening or this is review > > driven? I am wondering what would be the real effect of this mismatch? > > I have tried to follow to code path but I suspect > > split_huge_page_to_list would fail for hugetlbfs pages. If there is a > > more serious effect then we should mark the patch for stable as well. > > split_huge_page_to_list() fails on HugeTLB pages. I was experimenting around > moving 32MB contig HugeTLB pages on arm64 (with a debug patch applied) hit > the following stack trace when the kernel crashed. > > [ 3732.462797] Call trace: > [ 3732.462835] split_huge_page_to_list+0x3b0/0x858 > [ 3732.462913] migrate_pages+0x728/0xc20 > [ 3732.462999] soft_offline_page+0x448/0x8b0 > [ 3732.463097] __arm64_sys_madvise+0x724/0x850 > [ 3732.463197] el0_svc_handler+0x74/0x110 > [ 3732.463297] el0_svc+0x8/0xc > [ 3732.463347] Code: d1000400 f90b0e60 f2fbd5a2 a94982a1 (f9000420) Please make sure this makes it to the changelog and mark the patch for stable. -- Michal Hocko SUSE Labs