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>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ganesh Goudar <ganeshgr@linux.ibm.com>,
Allison Randal <allison@lohutok.net>,
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 v3 00/11] Introduces new count-based method for monitoring lockless pagetable walks
Date: Tue, 24 Sep 2019 18:24:17 -0300 [thread overview]
Message-ID: <20190924212427.7734-1-leonardo@linux.ibm.com> (raw)
If a process (qemu) with a lot of CPUs (128) try to munmap() a large
chunk of memory (496GB) mapped with THP, it takes an average of 275
seconds, which can cause a lot of problems to the load (in qemu case,
the guest will lock for this time).
Trying to find the source of this bug, I found out most of this time is
spent on serialize_against_pte_lookup(). This function will take a lot
of time in smp_call_function_many() if there is more than a couple CPUs
running the user process. Since it has to happen to all THP mapped, it
will take a very long time for large amounts of memory.
By the docs, serialize_against_pte_lookup() is needed in order to avoid
pmd_t to pte_t casting inside find_current_mm_pte(), or any lockless
pagetable walk, to happen concurrently with THP splitting/collapsing.
It does so by calling a do_nothing() on each CPU in mm->cpu_bitmap[],
after interrupts are re-enabled.
Since, interrupts are (usually) disabled during lockless pagetable
walk, and serialize_against_pte_lookup will only return after
interrupts are enabled, it is protected.
So, by what I could understand, if there is no lockless pagetable walk
running, there is no need to call serialize_against_pte_lookup().
So, to avoid the cost of running serialize_against_pte_lookup(), I
propose a counter that keeps track of how many find_current_mm_pte()
are currently running, and if there is none, just skip
smp_call_function_many().
The related functions are:
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
On my workload (qemu), I could see munmap's time reduction from 275
seconds to 418ms.
Changes since v2:
Rebased to v5.3
Adds support on __get_user_pages_fast
Adds usage decription to *_lockless_pgtbl_walk()
Better style to dummy functions
Link: http://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=131839
Changes since v1:
Isolated atomic operations in functions *_lockless_pgtbl_walk()
Fixed behavior of decrementing before last ptep was used
Link: http://patchwork.ozlabs.org/patch/1163093/
Leonardo Bras (11):
powerpc/mm: Adds counting method to monitor lockless pgtable walks
asm-generic/pgtable: Adds dummy functions to monitor lockless pgtable
walks
mm/gup: Applies counting method to monitor gup_pgd_range
powerpc/mce_power: Applies counting method to monitor lockless pgtbl
walks
powerpc/perf: Applies counting method to monitor lockless pgtbl walks
powerpc/mm/book3s64/hash: Applies counting method to monitor lockless
pgtbl walks
powerpc/kvm/e500: Applies counting method to monitor lockless pgtbl
walks
powerpc/kvm/book3s_hv: Applies counting method to monitor lockless
pgtbl walks
powerpc/kvm/book3s_64: Applies counting method to monitor lockless
pgtbl walks
powerpc/book3s_64: Enables counting method to monitor lockless pgtbl
walk
powerpc/mm/book3s64/pgtable: Uses counting method to skip serializing
arch/powerpc/include/asm/book3s/64/mmu.h | 3 ++
arch/powerpc/include/asm/book3s/64/pgtable.h | 5 +++
arch/powerpc/kernel/mce_power.c | 13 +++++--
arch/powerpc/kvm/book3s_64_mmu_hv.c | 2 +
arch/powerpc/kvm/book3s_64_mmu_radix.c | 20 +++++++++-
arch/powerpc/kvm/book3s_64_vio_hv.c | 4 ++
arch/powerpc/kvm/book3s_hv_nested.c | 8 ++++
arch/powerpc/kvm/book3s_hv_rm_mmu.c | 9 ++++-
arch/powerpc/kvm/e500_mmu_host.c | 4 ++
arch/powerpc/mm/book3s64/hash_tlb.c | 2 +
arch/powerpc/mm/book3s64/hash_utils.c | 7 ++++
arch/powerpc/mm/book3s64/mmu_context.c | 1 +
arch/powerpc/mm/book3s64/pgtable.c | 40 +++++++++++++++++++-
arch/powerpc/perf/callchain.c | 5 ++-
include/asm-generic/pgtable.h | 15 ++++++++
mm/gup.c | 8 ++++
16 files changed, 138 insertions(+), 8 deletions(-)
--
2.20.1
next reply other threads:[~2019-09-24 21:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-24 21:24 Leonardo Bras [this message]
2019-09-24 21:24 ` [PATCH v3 01/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks Leonardo Bras
2019-09-24 21:24 ` [PATCH v3 02/11] asm-generic/pgtable: Adds dummy functions " 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
2019-09-27 14:46 [PATCH v3 00/11] Introduces new count-based method for monitoring lockless pagetable walks Leonardo Bras
2019-09-27 23:25 ` Leonardo Bras
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