From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752867AbcBOLCS (ORCPT ); Mon, 15 Feb 2016 06:02:18 -0500 Received: from e19.ny.us.ibm.com ([129.33.205.209]:54240 "EHLO e19.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750925AbcBOLCQ convert rfc822-to-8bit (ORCPT ); Mon, 15 Feb 2016 06:02:16 -0500 X-IBM-Helo: d01dlp01.pok.ibm.com X-IBM-MailFrom: aneesh.kumar@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org From: "Aneesh Kumar K.V" To: Balbir Singh , benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, akpm@linux-foundation.org, Mel Gorman , "Kirill A. Shutemov" Cc: linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP update In-Reply-To: <1455512997.16012.24.camel@gmail.com> References: <1454980831-16631-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1455504278.16012.18.camel@gmail.com> <87lh6mfv2j.fsf@linux.vnet.ibm.com> <1455512997.16012.24.camel@gmail.com> User-Agent: Notmuch/0.20.2 (http://notmuchmail.org) Emacs/24.5.1 (x86_64-pc-linux-gnu) Date: Mon, 15 Feb 2016 16:31:59 +0530 Message-ID: <87d1ryfd94.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16021511-0057-0000-0000-0000036D2F6D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Balbir Singh writes: >> Now we can't depend for mm_cpumask, a parallel find_linux_pte_hugepte >> can happen outside that. Now i had a variant for kick_all_cpus_sync that >> ignored idle cpus. But then that needs more verification. >> >> http://article.gmane.org/gmane.linux.ports.ppc.embedded/81105 > Can be racy as a CPU moves from non-idle to idle > > In > >> +     pmd_hugepage_update(vma->vm_mm, address, pmdp, ~0UL, 0); >> +     /* >> +      * This ensures that generic code that rely on IRQ disabling >> +      * to prevent a parallel THP split work as expected. >> +      */ >> +     kick_all_cpus_sync(); > > pmdp_invalidate()->pmd_hugepage_update() can still run in parallel with  > find_linux_pte_or_hugepte() and race.. Am I missing something? > Yes. But then we make sure that the pte_t returned by find_linux_pte_or_hugepte doesn't change to a regular pmd entry by using that kick. Now callers of find_lnux_pte_or_hugepte will check for _PAGE_PRESENT. So if it called before pmd_hugepage_update(_PAGE_PRESENT), we wait for the caller to finish the usage (via kick()). Or they bail out after finding _PAGE_PRESENT cleared. -aneesh