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Tue, 24 Sep 2019 21:24:51 +0000 Received: from b03ledav006.gho.boulder.ibm.com (b03ledav006.gho.boulder.ibm.com [9.17.130.237]) by b03cxnp08026.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x8OLOnUS46530950 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 24 Sep 2019 21:24:49 GMT Received: from b03ledav006.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 92E86C6057; Tue, 24 Sep 2019 21:24:49 +0000 (GMT) Received: from b03ledav006.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id EDF7BC6059; Tue, 24 Sep 2019 21:24:44 +0000 (GMT) Received: from LeoBras.aus.stglabs.ibm.com (unknown [9.18.235.184]) by b03ledav006.gho.boulder.ibm.com (Postfix) with ESMTP; Tue, 24 Sep 2019 21:24:44 +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 , Greg Kroah-Hartman , Thomas Gleixner , Ganesh Goudar , Allison Randal , Mike Rapoport , YueHaibing , Ira Weiny , Jason Gunthorpe , John Hubbard , Keith Busch Subject: [PATCH v3 01/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks Date: Tue, 24 Sep 2019 18:24:18 -0300 Message-Id: <20190924212427.7734-2-leonardo@linux.ibm.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190924212427.7734-1-leonardo@linux.ibm.com> References: <20190924212427.7734-1-leonardo@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-09-24_10:,, 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-1909240173 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: It's necessary to monitor lockless pagetable walks, in order to avoid doi= ng 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 | 37 ++++++++++++++++++++++++ 3 files changed, 41 insertions(+) diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/incl= ude/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; =20 + /* Number of running instances of lockless pagetable walk*/ + atomic_t lockless_pgtbl_walk_count; + struct hash_mm_context *hash_context; =20 unsigned long vdso_base; diff --git a/arch/powerpc/mm/book3s64/mmu_context.c b/arch/powerpc/mm/boo= k3s64/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); =20 return 0; } diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s6= 4/pgtable.c index 7d0e0d0d22c4..0b86884a8097 100644 --- a/arch/powerpc/mm/book3s64/pgtable.c +++ b/arch/powerpc/mm/book3s64/pgtable.c @@ -98,6 +98,43 @@ void serialize_against_pte_lookup(struct mm_struct *mm= ) smp_call_function_many(mm_cpumask(mm), do_nothing, NULL, 1); } =20 +/* + * Counting method to monitor lockless pagetable walks: + * Uses start_lockless_pgtbl_walk and end_lockless_pgtbl_walk to track t= he + * 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 th= at 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); +} +EXPORT_SYMBOL(start_lockless_pgtbl_walk); + +/* + * end_lockless_pgtbl_walk: Must be inserted after the last use of a poi= nter + * returned by a lockless pagetable walk, such as __find_linux_pte() +*/ +void end_lockless_pgtbl_walk(struct mm_struct *mm) +{ + 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 w= alk, and + * THP split/collapse can be safely done. This can be used to avoid mo= re + * 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. --=20 2.20.1