From patchwork Fri Sep 27 23:39:58 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Leonardo Bras X-Patchwork-Id: 1168763 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=kvm-ppc-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=linux.ibm.com Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 46g7bX4lgtz9sQn for ; Sat, 28 Sep 2019 09:41:12 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728468AbfI0XlL (ORCPT ); Fri, 27 Sep 2019 19:41:11 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:52010 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725990AbfI0XlK (ORCPT ); Fri, 27 Sep 2019 19:41:10 -0400 Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x8RNbUe8012402; Fri, 27 Sep 2019 19:40:30 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 2v9u0p9mx9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 27 Sep 2019 19:40:30 -0400 Received: from m0098393.ppops.net (m0098393.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.27/8.16.0.27) with SMTP id x8RNbbf7012938; Fri, 27 Sep 2019 19:40:30 -0400 Received: from ppma02dal.us.ibm.com (a.bd.3ea9.ip4.static.sl-reverse.com [169.62.189.10]) by mx0a-001b2d01.pphosted.com with ESMTP id 2v9u0p9mx2-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 27 Sep 2019 19:40:30 -0400 Received: from pps.filterd (ppma02dal.us.ibm.com [127.0.0.1]) by ppma02dal.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x8RNeQkB024558; Fri, 27 Sep 2019 23:40:29 GMT Received: from b01cxnp23033.gho.pok.ibm.com (b01cxnp23033.gho.pok.ibm.com [9.57.198.28]) by ppma02dal.us.ibm.com with ESMTP id 2v5bg8k662-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 27 Sep 2019 23:40:29 +0000 Received: from b01ledav004.gho.pok.ibm.com (b01ledav004.gho.pok.ibm.com [9.57.199.109]) by b01cxnp23033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x8RNeSeh51380510 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 27 Sep 2019 23:40:28 GMT Received: from b01ledav004.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 107F6112069; Fri, 27 Sep 2019 23:40:28 +0000 (GMT) Received: from b01ledav004.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 615A1112062; Fri, 27 Sep 2019 23:40:24 +0000 (GMT) Received: from LeoBras.aus.stglabs.ibm.com (unknown [9.18.235.58]) by b01ledav004.gho.pok.ibm.com (Postfix) with ESMTP; Fri, 27 Sep 2019 23:40:24 +0000 (GMT) From: Leonardo Bras To: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org Cc: Leonardo Bras , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Arnd Bergmann , "Aneesh Kumar K.V" , Christophe Leroy , Andrew Morton , Dan Williams , Nicholas Piggin , Mahesh Salgaonkar , Allison Randal , Thomas Gleixner , Ganesh Goudar , Mike Rapoport , YueHaibing , Greg Kroah-Hartman , Ira Weiny , Jason Gunthorpe , John Hubbard , Keith Busch Subject: [PATCH v4 01/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks Date: Fri, 27 Sep 2019 20:39:58 -0300 Message-Id: <20190927234008.11513-2-leonardo@linux.ibm.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190927234008.11513-1-leonardo@linux.ibm.com> References: <20190927234008.11513-1-leonardo@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-09-27_09:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1909270205 Sender: kvm-ppc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm-ppc@vger.kernel.org It's necessary to monitor lockless pagetable walks, in order to avoid doing THP splitting/collapsing during them. Some methods rely on local_irq_{save,restore}, but that can be slow on cases with a lot of cpus are used for the process. In order to speedup some cases, I propose a refcount-based approach, that counts the number of lockless pagetable walks happening on the process. This method does not exclude the current irq-oriented method. It works as a complement to skip unnecessary waiting. start_lockless_pgtbl_walk(mm) Insert before starting any lockless pgtable walk end_lockless_pgtbl_walk(mm) Insert after the end of any lockless pgtable walk (Mostly after the ptep is last used) running_lockless_pgtbl_walk(mm) Returns the number of lockless pgtable walks running Signed-off-by: Leonardo Bras --- arch/powerpc/include/asm/book3s/64/mmu.h | 3 ++ arch/powerpc/mm/book3s64/mmu_context.c | 1 + arch/powerpc/mm/book3s64/pgtable.c | 45 ++++++++++++++++++++++++ 3 files changed, 49 insertions(+) diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h index 23b83d3593e2..13b006e7dde4 100644 --- a/arch/powerpc/include/asm/book3s/64/mmu.h +++ b/arch/powerpc/include/asm/book3s/64/mmu.h @@ -116,6 +116,9 @@ typedef struct { /* Number of users of the external (Nest) MMU */ atomic_t copros; + /* Number of running instances of lockless pagetable walk*/ + atomic_t lockless_pgtbl_walk_count; + struct hash_mm_context *hash_context; unsigned long vdso_base; diff --git a/arch/powerpc/mm/book3s64/mmu_context.c b/arch/powerpc/mm/book3s64/mmu_context.c index 2d0cb5ba9a47..3dd01c0ca5be 100644 --- a/arch/powerpc/mm/book3s64/mmu_context.c +++ b/arch/powerpc/mm/book3s64/mmu_context.c @@ -200,6 +200,7 @@ int init_new_context(struct task_struct *tsk, struct mm_struct *mm) #endif atomic_set(&mm->context.active_cpus, 0); atomic_set(&mm->context.copros, 0); + atomic_set(&mm->context.lockless_pgtbl_walk_count, 0); return 0; } diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s64/pgtable.c index 7d0e0d0d22c4..6ba6195bff1b 100644 --- a/arch/powerpc/mm/book3s64/pgtable.c +++ b/arch/powerpc/mm/book3s64/pgtable.c @@ -98,6 +98,51 @@ void serialize_against_pte_lookup(struct mm_struct *mm) smp_call_function_many(mm_cpumask(mm), do_nothing, NULL, 1); } +/* + * Counting method to monitor lockless pagetable walks: + * Uses start_lockless_pgtbl_walk and end_lockless_pgtbl_walk to track the + * number of lockless pgtable walks happening, and + * running_lockless_pgtbl_walk to return this value. + */ + +/* start_lockless_pgtbl_walk: Must be inserted before a function call that does + * lockless pagetable walks, such as __find_linux_pte() + */ +void start_lockless_pgtbl_walk(struct mm_struct *mm) +{ + atomic_inc(&mm->context.lockless_pgtbl_walk_count); + /* Avoid reorder to garantee that the increment will happen before any + * part of the walkless pagetable walk after it. + */ + smp_mb(); +} +EXPORT_SYMBOL(start_lockless_pgtbl_walk); + +/* + * end_lockless_pgtbl_walk: Must be inserted after the last use of a pointer + * returned by a lockless pagetable walk, such as __find_linux_pte() +*/ +void end_lockless_pgtbl_walk(struct mm_struct *mm) +{ + /* Avoid reorder to garantee that it will only decrement after the last + * use of the returned ptep from the lockless pagetable walk. + */ + smp_mb(); + atomic_dec(&mm->context.lockless_pgtbl_walk_count); +} +EXPORT_SYMBOL(end_lockless_pgtbl_walk); + +/* + * running_lockless_pgtbl_walk: Returns the number of lockless pagetable walks + * currently running. If it returns 0, there is no running pagetable walk, and + * THP split/collapse can be safely done. This can be used to avoid more + * expensive approaches like serialize_against_pte_lookup() + */ +int running_lockless_pgtbl_walk(struct mm_struct *mm) +{ + return atomic_read(&mm->context.lockless_pgtbl_walk_count); +} + /* * We use this to invalidate a pmdp entry before switching from a * hugepte to regular pmd entry.