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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
Subject: [PATCH v5 10/11] mm/Kconfig: Adds config option to track lockless
 pagetable walks
Date: Wed,  2 Oct 2019 22:33:24 -0300
Message-Id: <20191003013325.2614-11-leonardo@linux.ibm.com>
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Cc: Song Liu <songliubraving@fb.com>, Michal Hocko <mhocko@suse.com>,
 "Peter Zijlstra \(Intel\)" <peterz@infradead.org>,
 "Dmitry V. Levin" <ldv@altlinux.org>, Keith Busch <keith.busch@intel.com>,
 Paul Mackerras <paulus@samba.org>, Christoph Lameter <cl@linux.com>,
 Ira Weiny <ira.weiny@intel.com>, Thomas Gleixner <tglx@linutronix.de>,
 Elena Reshetova <elena.reshetova@intel.com>,
 Andrea Arcangeli <aarcange@redhat.com>, Santosh Sivaraj <santosh@fossix.org>,
 Davidlohr Bueso <dave@stgolabs.net>,
 "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
 Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
 Mike Rapoport <rppt@linux.ibm.com>, Jason Gunthorpe <jgg@ziepe.ca>,
 Allison Randal <allison@lohutok.net>,
 Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
 Leonardo Bras <leonardo@linux.ibm.com>, Alexey Dobriyan <adobriyan@gmail.com>,
 Ingo Molnar <mingo@kernel.org>, Ralph Campbell <rcampbell@nvidia.com>,
 Arnd Bergmann <arnd@arndb.de>, Jann Horn <jannh@google.com>,
 John Hubbard <jhubbard@nvidia.com>, Jesper Dangaard Brouer <brouer@redhat.com>,
 Nicholas Piggin <npiggin@gmail.com>,
 =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= <jglisse@redhat.com>,
 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
 Al Viro <viro@zeniv.linux.org.uk>, Andrey Ryabinin <aryabinin@virtuozzo.com>,
 Dan Williams <dan.j.williams@intel.com>, Reza Arbab <arbab@linux.ibm.com>,
 Vlastimil Babka <vbabka@suse.cz>,
 Christian Brauner <christian.brauner@ubuntu.com>,
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Souptick Joarder <jrdr.linux@gmail.com>,
 Andrew Morton <akpm@linux-foundation.org>,
 Logan Gunthorpe <logang@deltatee.com>, Roman Gushchin <guro@fb.com>,
 "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
Sender: "Linuxppc-dev"
 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

Adds config option LOCKLESS_PAGE_TABLE_WALK_TRACKING to make possible
enabling tracking lockless pagetable walks directly from kernel config.

Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
---
 mm/Kconfig | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/Kconfig b/mm/Kconfig
index a5dae9a7eb51..00f487a0122f 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -736,4 +736,15 @@ config ARCH_HAS_PTE_SPECIAL
 config ARCH_HAS_HUGEPD
 	bool
 
+config LOCKLESS_PAGE_TABLE_WALK_TRACKING
+	bool "Track (and optimize) lockless page table walks"
+	default n
+
+	help
+	  Maintain a reference count of active lockless page table
+	  walkers. This adds 4 bytes to struct mm size, and two atomic
+	  operations to calls such as get_user_pages_fast(). Some
+	  architectures can optimize lockless page table operations if
+	  this is enabled.
+
 endmenu
-- 
2.20.1