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: Keith Busch <keith.busch@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Ganesh Goudar <ganeshgr@linux.ibm.com>,
YueHaibing <yuehaibing@huawei.com>,
Nicholas Piggin <npiggin@gmail.com>,
Mike Rapoport <rppt@linux.ibm.com>,
Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
Jason Gunthorpe <jgg@ziepe.ca>, Paul Mackerras <paulus@samba.org>,
John Hubbard <jhubbard@nvidia.com>,
Leonardo Bras <leonardo@linux.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Ira Weiny <ira.weiny@intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Allison Randal <allison@lohutok.net>
Subject: [PATCH v3 01/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks
Date: Tue, 24 Sep 2019 18:24:18 -0300 [thread overview]
Message-ID: <20190924212427.7734-2-leonardo@linux.ibm.com> (raw)
In-Reply-To: <20190924212427.7734-1-leonardo@linux.ibm.com>
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 <leonardo@linux.ibm.com>
---
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/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..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);
}
+/*
+ * 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);
+}
+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)
+{
+ 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.
--
2.20.1
next prev parent reply other threads:[~2019-09-24 21:31 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-24 21:24 [PATCH v3 00/11] Introduces new count-based method for monitoring lockless pagetable walks Leonardo Bras
2019-09-24 21:24 ` Leonardo Bras [this message]
2019-09-24 21:24 ` [PATCH v3 02/11] asm-generic/pgtable: Adds dummy functions to monitor lockless pgtable walks Leonardo Bras
2019-09-24 21:24 ` [PATCH v3 03/11] mm/gup: Applies counting method to monitor gup_pgd_range Leonardo Bras
2019-09-24 21:24 ` [PATCH v3 04/11] powerpc/mce_power: Applies counting method to monitor lockless pgtbl walks Leonardo Bras
2019-09-24 21:24 ` [PATCH v3 05/11] powerpc/perf: " Leonardo Bras
2019-09-24 21:24 ` [PATCH v3 06/11] powerpc/mm/book3s64/hash: " Leonardo Bras
2019-09-24 21:24 ` [PATCH v3 07/11] powerpc/kvm/e500: " Leonardo Bras
2019-09-24 21:24 ` [PATCH v3 08/11] powerpc/kvm/book3s_hv: " Leonardo Bras
2019-09-24 21:24 ` [PATCH v3 09/11] powerpc/kvm/book3s_64: " Leonardo Bras
2019-09-24 21:24 ` [PATCH v3 10/11] powerpc/book3s_64: Enables counting method to monitor lockless pgtbl walk Leonardo Bras
2019-09-24 21:24 ` [PATCH v3 11/11] powerpc/mm/book3s64/pgtable: Uses counting method to skip serializing Leonardo Bras
2019-09-24 22:58 ` [PATCH v3 00/11] Introduces new count-based method for monitoring lockless pagetable walks John Hubbard
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