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From:   Leonardo Bras <leonardo@linux.ibm.com>
To:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.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>,
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        "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>,
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        Richard Fontana <rfontana@redhat.com>,
        Ganesh Goudar <ganeshgr@linux.ibm.com>,
        Allison Randal <allison@lohutok.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        YueHaibing <yuehaibing@huawei.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        John Hubbard <jhubbard@nvidia.com>,
        Keith Busch <keith.busch@intel.com>
Subject: [PATCH v2 03/11] mm/gup: Applies counting method to monitor gup_pgd_range
Date:   Fri, 20 Sep 2019 16:50:39 -0300
Message-Id: <20190920195047.7703-4-leonardo@linux.ibm.com>
In-Reply-To: <20190920195047.7703-1-leonardo@linux.ibm.com>
References: <20190920195047.7703-1-leonardo@linux.ibm.com>
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As decribed, gup_pgd_range is a lockless pagetable walk. So, in order to
monitor against THP split/collapse with the couting method, it's necessary
to bound it with {start,end}_lockless_pgtbl_walk.

There are dummy functions, so it is not going to add any overhead on archs
that don't use this method.

Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
---
 mm/gup.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index 98f13ab37bac..675e4be27082 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2404,6 +2404,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
 			unsigned int gup_flags, struct page **pages)
 {
 	unsigned long addr, len, end;
+	struct mm_struct *mm;
 	int nr = 0, ret = 0;
 
 	if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM)))
@@ -2421,9 +2422,12 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
 
 	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) &&
 	    gup_fast_permitted(start, end)) {
+		mm = current->mm;
+		start_lockless_pgtbl_walk(mm);
 		local_irq_disable();
 		gup_pgd_range(addr, end, gup_flags, pages, &nr);
 		local_irq_enable();
+		end_lockless_pgtbl_walk(mm);
 		ret = nr;
 	}
 
-- 
2.20.1