Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Leonardo Bras <leonardo@linux.ibm.com>
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 <leonardo@linux.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Arnd Bergmann <arnd@arndb.de>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
        Allison Randal <allison@lohutok.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ganesh Goudar <ganeshgr@linux.ibm.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        YueHaibing <yuehaibing@huawei.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ira Weiny <ira.weiny@intel.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        John Hubbard <jhubbard@nvidia.com>,
        Keith Busch <keith.busch@intel.com>
Subject: [PATCH v4 02/11] asm-generic/pgtable: Adds dummy functions to monitor lockless pgtable walks
Date:   Fri, 27 Sep 2019 20:39:59 -0300
Message-Id: <20190927234008.11513-3-leonardo@linux.ibm.com>
In-Reply-To: <20190927234008.11513-1-leonardo@linux.ibm.com>
References: <20190927234008.11513-1-leonardo@linux.ibm.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

There is a need 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 these cases, I propose a refcount-based approach, that
counts the number of lockless pagetable	walks happening on the process.

Given that there are lockless pagetable walks on generic code, it's
necessary to create dummy functions for archs that won't use the approach.

Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
---
 include/asm-generic/pgtable.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 75d9d68a6de7..0831475e72d3 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -1172,6 +1172,21 @@ static inline bool arch_has_pfn_modify_check(void)
 #endif
 #endif
 
+#ifndef __HAVE_ARCH_LOCKLESS_PGTBL_WALK_COUNTER
+static inline void start_lockless_pgtbl_walk(struct mm_struct *mm)
+{
+}
+
+static inline void end_lockless_pgtbl_walk(struct mm_struct *mm)
+{
+}
+
+static inline int running_lockless_pgtbl_walk(struct mm_struct *mm)
+{
+	return 0;
+}
+#endif
+
 /*
  * On some architectures it depends on the mm if the p4d/pud or pmd
  * layer of the page table hierarchy is folded or not.
-- 
2.20.1