From: John Hubbard <jhubbard@nvidia.com> To: Leonardo Bras <leonardo@linux.ibm.com>, <linuxppc-dev@lists.ozlabs.org>, <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org> Cc: 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>, Thomas Gleixner <tglx@linutronix.de>, 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>, Keith Busch <keith.busch@intel.com> Subject: Re: [PATCH v2 01/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks Date: Mon, 23 Sep 2019 13:42:44 -0700 [thread overview] Message-ID: <90ceb0ca-9f04-65a5-586c-e37c2ecc6e4e@nvidia.com> (raw) In-Reply-To: <20190920195047.7703-2-leonardo@linux.ibm.com> On 9/20/19 12:50 PM, Leonardo Bras wrote: > 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 | 17 +++++++++++++++++ > 3 files changed, 21 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..13239b17a22c 100644 > --- a/arch/powerpc/mm/book3s64/pgtable.c > +++ b/arch/powerpc/mm/book3s64/pgtable.c > @@ -98,6 +98,23 @@ void serialize_against_pte_lookup(struct mm_struct *mm) > smp_call_function_many(mm_cpumask(mm), do_nothing, NULL, 1); > } > Somewhere, there should be a short comment that explains how the following functions are meant to be used. And it should include the interaction with irqs, so maybe if you end up adding that combined wrapper function that does both, that's where the documentation would go. If not, then here is probably where it goes. > +void start_lockless_pgtbl_walk(struct mm_struct *mm) > +{ > + atomic_inc(&mm->context.lockless_pgtbl_walk_count); > +} > +EXPORT_SYMBOL(start_lockless_pgtbl_walk); > + > +void end_lockless_pgtbl_walk(struct mm_struct *mm) > +{ > + atomic_dec(&mm->context.lockless_pgtbl_walk_count); > +} > +EXPORT_SYMBOL(end_lockless_pgtbl_walk); > + > +int running_lockless_pgtbl_walk(struct mm_struct *mm) > +{ > + return atomic_read(&mm->context.lockless_pgtbl_walk_count); > +} > + thanks, -- John Hubbard NVIDIA
WARNING: multiple messages have this Message-ID (diff)
From: John Hubbard <jhubbard@nvidia.com> To: Leonardo Bras <leonardo@linux.ibm.com>, <linuxppc-dev@lists.ozlabs.org>, <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org> Cc: Jason Gunthorpe <jgg@ziepe.ca>, Thomas Gleixner <tglx@linutronix.de>, Arnd Bergmann <arnd@arndb.de>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, YueHaibing <yuehaibing@huawei.com>, Keith Busch <keith.busch@intel.com>, Nicholas Piggin <npiggin@gmail.com>, Mike Rapoport <rppt@linux.ibm.com>, Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>, Richard Fontana <rfontana@redhat.com>, Paul Mackerras <paulus@samba.org>, "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>, Ganesh Goudar <ganeshgr@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: Re: [PATCH v2 01/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks Date: Mon, 23 Sep 2019 13:42:44 -0700 [thread overview] Message-ID: <90ceb0ca-9f04-65a5-586c-e37c2ecc6e4e@nvidia.com> (raw) In-Reply-To: <20190920195047.7703-2-leonardo@linux.ibm.com> On 9/20/19 12:50 PM, Leonardo Bras wrote: > 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 | 17 +++++++++++++++++ > 3 files changed, 21 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..13239b17a22c 100644 > --- a/arch/powerpc/mm/book3s64/pgtable.c > +++ b/arch/powerpc/mm/book3s64/pgtable.c > @@ -98,6 +98,23 @@ void serialize_against_pte_lookup(struct mm_struct *mm) > smp_call_function_many(mm_cpumask(mm), do_nothing, NULL, 1); > } > Somewhere, there should be a short comment that explains how the following functions are meant to be used. And it should include the interaction with irqs, so maybe if you end up adding that combined wrapper function that does both, that's where the documentation would go. If not, then here is probably where it goes. > +void start_lockless_pgtbl_walk(struct mm_struct *mm) > +{ > + atomic_inc(&mm->context.lockless_pgtbl_walk_count); > +} > +EXPORT_SYMBOL(start_lockless_pgtbl_walk); > + > +void end_lockless_pgtbl_walk(struct mm_struct *mm) > +{ > + atomic_dec(&mm->context.lockless_pgtbl_walk_count); > +} > +EXPORT_SYMBOL(end_lockless_pgtbl_walk); > + > +int running_lockless_pgtbl_walk(struct mm_struct *mm) > +{ > + return atomic_read(&mm->context.lockless_pgtbl_walk_count); > +} > + thanks, -- John Hubbard NVIDIA
next prev parent reply other threads:[~2019-09-23 20:42 UTC|newest] Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-09-20 19:50 [PATCH v2 00/11] Introduces new count-based method for monitoring lockless pagetable wakls Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-20 19:50 ` [PATCH v2 01/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-23 20:42 ` John Hubbard [this message] 2019-09-23 20:42 ` John Hubbard 2019-09-23 20:50 ` Leonardo Bras 2019-09-23 20:50 ` Leonardo Bras 2019-09-20 19:50 ` [PATCH v2 02/11] asm-generic/pgtable: Adds dummy functions " Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-23 20:39 ` John Hubbard 2019-09-23 20:39 ` John Hubbard 2019-09-23 20:48 ` Leonardo Bras 2019-09-23 20:48 ` Leonardo Bras 2019-09-23 20:53 ` John Hubbard 2019-09-23 20:53 ` John Hubbard 2019-09-20 19:50 ` [PATCH v2 03/11] mm/gup: Applies counting method to monitor gup_pgd_range Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-23 20:27 ` John Hubbard 2019-09-23 20:27 ` John Hubbard 2019-09-23 21:01 ` Leonardo Bras 2019-09-23 21:01 ` Leonardo Bras 2019-09-23 21:09 ` John Hubbard 2019-09-23 21:09 ` John Hubbard 2019-09-20 19:50 ` [PATCH v2 04/11] powerpc/mce_power: Applies counting method to monitor lockless pgtbl walks Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-20 19:50 ` [PATCH v2 05/11] powerpc/perf: " Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-20 19:50 ` [PATCH v2 06/11] powerpc/mm/book3s64/hash: " Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-20 19:50 ` [PATCH v2 07/11] powerpc/kvm/e500: " Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-20 19:50 ` [PATCH v2 08/11] powerpc/kvm/book3s_hv: " Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-23 20:47 ` John Hubbard 2019-09-23 20:47 ` John Hubbard 2019-09-20 19:50 ` [PATCH v2 09/11] powerpc/kvm/book3s_64: " Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-20 19:50 ` [PATCH v2 10/11] powerpc/book3s_64: Enables counting method to monitor lockless pgtbl walk Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-20 19:50 ` [PATCH v2 11/11] powerpc/mm/book3s64/pgtable: Uses counting method to skip serializing Leonardo Bras 2019-09-20 19:50 ` Leonardo Bras 2019-09-20 20:11 ` John Hubbard 2019-09-20 20:28 ` Leonardo Bras 2019-09-20 20:28 ` Leonardo Bras 2019-09-20 21:15 ` John Hubbard 2019-09-21 0:48 ` John Hubbard 2019-09-21 0:48 ` John Hubbard 2019-09-23 17:25 ` Leonardo Bras 2019-09-23 17:25 ` Leonardo Bras 2019-09-23 18:14 ` John Hubbard 2019-09-23 18:14 ` John Hubbard 2019-09-23 19:40 ` Leonardo Bras 2019-09-23 19:40 ` Leonardo Bras 2019-09-23 19:58 ` John Hubbard 2019-09-23 19:58 ` John Hubbard 2019-09-23 20:23 ` Leonardo Bras 2019-09-23 20:23 ` Leonardo Bras 2019-09-23 20:26 ` John Hubbard 2019-09-23 20:26 ` John Hubbard 2019-09-20 19:56 ` [PATCH v2 00/11] Introduces new count-based method for monitoring lockless pagetable wakls Leonardo Bras 2019-09-20 19:56 ` Leonardo Bras 2019-09-20 20:12 ` Leonardo Bras 2019-09-20 20:12 ` Leonardo Bras 2019-09-20 21:24 ` John Hubbard 2019-09-20 21:24 ` John Hubbard 2019-09-23 20:51 ` John Hubbard 2019-09-23 20:51 ` John Hubbard 2019-09-23 20:58 ` Leonardo Bras 2019-09-23 20:58 ` Leonardo Bras
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