From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qg0-f45.google.com (mail-qg0-f45.google.com [209.85.192.45]) by kanga.kvack.org (Postfix) with ESMTP id 6DC78828DF for ; Mon, 15 Feb 2016 06:02:15 -0500 (EST) Received: by mail-qg0-f45.google.com with SMTP id b67so107672283qgb.1 for ; Mon, 15 Feb 2016 03:02:15 -0800 (PST) Received: from e17.ny.us.ibm.com (e17.ny.us.ibm.com. [129.33.205.207]) by mx.google.com with ESMTPS id s2si33756062qki.76.2016.02.15.03.02.14 for (version=TLS1_2 cipher=AES128-SHA bits=128/128); Mon, 15 Feb 2016 03:02:14 -0800 (PST) Received: from localhost by e17.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 15 Feb 2016 06:02:14 -0500 Received: from b01cxnp23033.gho.pok.ibm.com (b01cxnp23033.gho.pok.ibm.com [9.57.198.28]) by d01dlp01.pok.ibm.com (Postfix) with ESMTP id 050C338C8041 for ; Mon, 15 Feb 2016 06:02:12 -0500 (EST) Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by b01cxnp23033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u1FB2BcN32571410 for ; Mon, 15 Feb 2016 11:02:11 GMT Received: from d01av04.pok.ibm.com (localhost [127.0.0.1]) by d01av04.pok.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u1FB2A8q030500 for ; Mon, 15 Feb 2016 06:02:11 -0500 From: "Aneesh Kumar K.V" 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> 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: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: 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 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. >>=20 >> http://article.gmane.org/gmane.linux.ports.ppc.embedded/81105 > Can be racy as a CPU moves from non-idle to idle > > In > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0pmd_hugepage_update(vma->vm_mm, address, = pmdp, ~0UL, 0); >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0/* >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0* This ensures that generic code th= at rely on IRQ disabling >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0* to prevent a parallel THP split w= ork as expected. >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0*/ >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0kick_all_cpus_sync(); > > pmdp_invalidate()->pmd_hugepage_update() can still run in parallel with= =C2=A0 > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org