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Subject[PATCH 2/2] mm: numa: Do not clear PTEs or PMDs for NUMA hinting faults
Date
Dave Chinner reported the following on https://lkml.org/lkml/2015/3/1/226

Across the board the 4.0-rc1 numbers are much slower, and the
degradation is far worse when using the large memory footprint
configs. Perf points straight at the cause - this is from 4.0-rc1
on the "-o bhash=101073" config:

- 56.07% 56.07% [kernel] [k] default_send_IPI_mask_sequence_phys
- default_send_IPI_mask_sequence_phys
- 99.99% physflat_send_IPI_mask
- 99.37% native_send_call_func_ipi
smp_call_function_many
- native_flush_tlb_others
- 99.85% flush_tlb_page
ptep_clear_flush
try_to_unmap_one
rmap_walk
try_to_unmap
migrate_pages
migrate_misplaced_page
- handle_mm_fault
- 99.73% __do_page_fault
trace_do_page_fault
do_async_page_fault
+ async_page_fault
0.63% native_send_call_func_single_ipi
generic_exec_single
smp_call_function_single

This was bisected to commit 4d9424669946 ("mm: convert p[te|md]_mknonnuma
and remaining page table manipulations") which clears PTEs and PMDs to make
them PROT_NONE. This is tidy but tests on some benchmarks indicate that
there are many more hinting faults trapped resulting in excessive migration.
This is the result for the old autonuma benchmark for example.

autonumabench
4.0.0-rc1 4.0.0-rc1 3.19.0
vanilla noclear-v1 vanilla
Time User-NUMA01 32883.59 ( 0.00%) 27401.21 ( 16.67%) 25695.96 ( 21.86%)
Time User-NUMA01_THEADLOCAL 17453.20 ( 0.00%) 17491.98 ( -0.22%) 17404.36 ( 0.28%)
Time User-NUMA02 2063.70 ( 0.00%) 2059.94 ( 0.18%) 2037.65 ( 1.26%)
Time User-NUMA02_SMT 983.70 ( 0.00%) 967.95 ( 1.60%) 981.02 ( 0.27%)
Time System-NUMA01 602.44 ( 0.00%) 182.16 ( 69.76%) 194.70 ( 67.68%)
Time System-NUMA01_THEADLOCAL 78.10 ( 0.00%) 84.84 ( -8.63%) 98.52 (-26.15%)
Time System-NUMA02 6.47 ( 0.00%) 9.74 (-50.54%) 9.28 (-43.43%)
Time System-NUMA02_SMT 5.06 ( 0.00%) 3.97 ( 21.54%) 3.79 ( 25.10%)
Time Elapsed-NUMA01 755.96 ( 0.00%) 602.20 ( 20.34%) 558.84 ( 26.08%)
Time Elapsed-NUMA01_THEADLOCAL 382.22 ( 0.00%) 384.98 ( -0.72%) 382.54 ( -0.08%)
Time Elapsed-NUMA02 49.38 ( 0.00%) 49.23 ( 0.30%) 49.83 ( -0.91%)
Time Elapsed-NUMA02_SMT 47.70 ( 0.00%) 46.82 ( 1.84%) 46.59 ( 2.33%)
Time CPU-NUMA01 4429.00 ( 0.00%) 4580.00 ( -3.41%) 4632.00 ( -4.58%)
Time CPU-NUMA01_THEADLOCAL 4586.00 ( 0.00%) 4565.00 ( 0.46%) 4575.00 ( 0.24%)
Time CPU-NUMA02 4191.00 ( 0.00%) 4203.00 ( -0.29%) 4107.00 ( 2.00%)
Time CPU-NUMA02_SMT 2072.00 ( 0.00%) 2075.00 ( -0.14%) 2113.00 ( -1.98%)

Note the system CPU usage with the patch applied and how it's similar to
3.19-vanilla. The NUMA hinting activity is also restored to similar levels.

4.0.0-rc1 4.0.0-rc1 3.19.0
vanillanoclear-v1r13 vanilla
NUMA alloc hit 1437560 1241466 1202922
NUMA alloc miss 0 0 0
NUMA interleave hit 0 0 0
NUMA alloc local 1436781 1240849 1200683
NUMA base PTE updates 304513172 223926293 222840103
NUMA huge PMD updates 594467 437025 434894
NUMA page range updates 608880276 447683093 445505831
NUMA hint faults 733491 598990 601358
NUMA hint local faults 511530 314936 371571
NUMA hint local percent 69 52 61
NUMA pages migrated 26366701 5424102 7073177

Signed-off-by: Mel Gorman <mgorman@suse.de>
---
arch/powerpc/include/asm/pgtable-ppc64.h | 16 ++++++++++++++++
arch/x86/include/asm/pgtable.h | 14 ++++++++++++++
include/asm-generic/pgtable.h | 19 +++++++++++++++++++
mm/huge_memory.c | 19 ++++++++++++++++---
mm/mprotect.c | 5 +++++
5 files changed, 70 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/pgtable-ppc64.h b/arch/powerpc/include/asm/pgtable-ppc64.h
index 43e6ad424c7f..bb654c192028 100644
--- a/arch/powerpc/include/asm/pgtable-ppc64.h
+++ b/arch/powerpc/include/asm/pgtable-ppc64.h
@@ -506,6 +506,22 @@ static inline pmd_t pmd_mkhuge(pmd_t pmd)
return pmd;
}

+#define pte_mkprotnone pte_mkprotnone
+static inline pte_t pte_mkprotnone(pte_t pte)
+{
+ pte_val(pte) &= ~_PAGE_PRESENT;
+ pte_val(pte) |= _PAGE_USER;
+ return pte;
+}
+
+#define pmd_mkprotnone pmd_mkprotnone
+static inline pmd_t pmd_mkprotnone(pmd_t pmd)
+{
+ pmd_val(pmd) &= ~_PAGE_PRESENT;
+ pmd_val(pmd) |= _PAGE_USER;
+ return pmd;
+}
+
static inline pmd_t pmd_mknotpresent(pmd_t pmd)
{
pmd_val(pmd) &= ~_PAGE_PRESENT;
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index a0c35bf6cb92..5524fa6f7e8e 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -292,6 +292,20 @@ static inline pmd_t pmd_mkwrite(pmd_t pmd)
return pmd_set_flags(pmd, _PAGE_RW);
}

+#define pte_mkprotnone pte_mkprotnone
+static inline pte_t pte_mkprotnone(pte_t pte)
+{
+ pte = pte_clear_flags(pte, _PAGE_PRESENT);
+ return pte_set_flags(pte, _PAGE_PROTNONE);
+}
+
+#define pmd_mkprotnone pmd_mkprotnone
+static inline pmd_t pmd_mkprotnone(pmd_t pmd)
+{
+ pmd = pmd_clear_flags(pmd, _PAGE_PRESENT);
+ return pmd_set_flags(pmd, _PAGE_PROTNONE);
+}
+
static inline pmd_t pmd_mknotpresent(pmd_t pmd)
{
return pmd_clear_flags(pmd, _PAGE_PRESENT | _PAGE_PROTNONE);
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 4d46085c1b90..837dbde26662 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -669,6 +669,25 @@ static inline int pmd_trans_unstable(pmd_t *pmd)
#endif
}

+#ifndef pte_mkprotnone
+/*
+ * Only automatic NUMA balancing needs this so arches that support it must
+ * define pte_mknotpresent.
+ */
+static inline pte_mkprotnone(pte_t pte)
+{
+ BUG();
+}
+#endif
+
+#ifndef pmd_mkprotnone
+static inline pmd_mkprotnone(pmd_t pmd)
+{
+ BUG();
+}
+#endif
+
+
#ifndef CONFIG_NUMA_BALANCING
/*
* Technically a PTE can be PROTNONE even when not doing NUMA balancing but
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 194c0f019774..d9d5a2045d10 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1495,11 +1495,24 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
}

if (!prot_numa || !pmd_protnone(*pmd)) {
- entry = pmdp_get_and_clear_notify(mm, addr, pmd);
- entry = pmd_modify(entry, newprot);
+ /*
+ * NUMA hinting update can avoid a clear and defer the
+ * flush as it is not a functional correctness issue if
+ * access occurs after the update and this avoids
+ * spurious faults.
+ */
+ if (prot_numa) {
+ entry = *pmd;
+ entry = pmd_mkprotnone(entry);
+ } else {
+ entry = pmdp_get_and_clear_notify(mm, addr,
+ pmd);
+ entry = pmd_modify(entry, newprot);
+ BUG_ON(pmd_write(entry));
+ }
+
ret = HPAGE_PMD_NR;
set_pmd_at(mm, addr, pmd, entry);
- BUG_ON(pmd_write(entry));
}
spin_unlock(ptl);
}
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 44727811bf4c..aa97d5cab6ce 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -90,6 +90,11 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
/* Avoid TLB flush if possible */
if (pte_protnone(oldpte))
continue;
+
+ ptent = pte_mkprotnone(oldpte);
+ set_pte_at(mm, addr, pte, ptent);
+ pages++;
+ continue;
}

ptent = ptep_modify_prot_start(mm, addr, pte);
--
2.1.2


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