From: Jérôme Glisse <jglisse@xxxxxxxxxx>
Subject: mm/mmu_notifier: avoid call to invalidate_range() in range_end()
This is an optimization patch that only affect mmu_notifier users which
rely on the invalidate_range() callback. This patch avoids calling that
callback twice in a row from inside __mmu_notifier_invalidate_range_end
Existing pattern (before this patch):
mmu_notifier_invalidate_range_start()
pte/pmd/pud_clear_flush_notify()
mmu_notifier_invalidate_range()
mmu_notifier_invalidate_range_end()
mmu_notifier_invalidate_range()
New pattern (after this patch):
mmu_notifier_invalidate_range_start()
pte/pmd/pud_clear_flush_notify()
mmu_notifier_invalidate_range()
mmu_notifier_invalidate_range_only_end()
We call the invalidate_range callback after clearing the page table under
the page table lock and we skip the call to invalidate_range inside the
__mmu_notifier_invalidate_range_end() function.
Idea from Andrea Arcangeli
Link: http://lkml.kernel.org/r/20171017031003.7481-3-jglisse@xxxxxxxxxx
Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Joerg Roedel <jroedel@xxxxxxx>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: Alistair Popple <alistair@xxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Andrew Donnellan <andrew.donnellan@xxxxxxxxxxx>
Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mmu_notifier.h | 17 ++++++++++--
mm/huge_memory.c | 46 ++++++++++++++++++++++++++++++---
mm/memory.c | 6 +++-
mm/migrate.c | 15 ++++++++--
mm/mmu_notifier.c | 11 ++++++-
5 files changed, 83 insertions(+), 12 deletions(-)
diff -puN include/linux/mmu_notifier.h~mm-mmu_notifier-avoid-call-to-invalidate_range-in-range_end include/linux/mmu_notifier.h
--- a/include/linux/mmu_notifier.h~mm-mmu_notifier-avoid-call-to-invalidate_range-in-range_end
+++ a/include/linux/mmu_notifier.h
@@ -214,7 +214,8 @@ extern void __mmu_notifier_change_pte(st
extern void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
unsigned long start, unsigned long end);
extern void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
- unsigned long start, unsigned long end);
+ unsigned long start, unsigned long end,
+ bool only_end);
extern void __mmu_notifier_invalidate_range(struct mm_struct *mm,
unsigned long start, unsigned long end);
@@ -268,7 +269,14 @@ static inline void mmu_notifier_invalida
unsigned long start, unsigned long end)
{
if (mm_has_notifiers(mm))
- __mmu_notifier_invalidate_range_end(mm, start, end);
+ __mmu_notifier_invalidate_range_end(mm, start, end, false);
+}
+
+static inline void mmu_notifier_invalidate_range_only_end(struct mm_struct *mm,
+ unsigned long start, unsigned long end)
+{
+ if (mm_has_notifiers(mm))
+ __mmu_notifier_invalidate_range_end(mm, start, end, true);
}
static inline void mmu_notifier_invalidate_range(struct mm_struct *mm,
@@ -438,6 +446,11 @@ static inline void mmu_notifier_invalida
unsigned long start, unsigned long end)
{
}
+
+static inline void mmu_notifier_invalidate_range_only_end(struct mm_struct *mm,
+ unsigned long start, unsigned long end)
+{
+}
static inline void mmu_notifier_invalidate_range(struct mm_struct *mm,
unsigned long start, unsigned long end)
diff -puN mm/huge_memory.c~mm-mmu_notifier-avoid-call-to-invalidate_range-in-range_end mm/huge_memory.c
--- a/mm/huge_memory.c~mm-mmu_notifier-avoid-call-to-invalidate_range-in-range_end
+++ a/mm/huge_memory.c
@@ -1223,7 +1223,12 @@ static int do_huge_pmd_wp_page_fallback(
page_remove_rmap(page, true);
spin_unlock(vmf->ptl);
- mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
+ /*
+ * No need to double call mmu_notifier->invalidate_range() callback as
+ * the above pmdp_huge_clear_flush_notify() did already call it.
+ */
+ mmu_notifier_invalidate_range_only_end(vma->vm_mm, mmun_start,
+ mmun_end);
ret |= VM_FAULT_WRITE;
put_page(page);
@@ -1372,7 +1377,12 @@ alloc:
}
spin_unlock(vmf->ptl);
out_mn:
- mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
+ /*
+ * No need to double call mmu_notifier->invalidate_range() callback as
+ * the above pmdp_huge_clear_flush_notify() did already call it.
+ */
+ mmu_notifier_invalidate_range_only_end(vma->vm_mm, mmun_start,
+ mmun_end);
out:
return ret;
out_unlock:
@@ -2024,7 +2034,12 @@ void __split_huge_pud(struct vm_area_str
out:
spin_unlock(ptl);
- mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PUD_SIZE);
+ /*
+ * No need to double call mmu_notifier->invalidate_range() callback as
+ * the above pudp_huge_clear_flush_notify() did already call it.
+ */
+ mmu_notifier_invalidate_range_only_end(mm, haddr, haddr +
+ HPAGE_PUD_SIZE);
}
#endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
@@ -2099,6 +2114,15 @@ static void __split_huge_pmd_locked(stru
add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
return;
} else if (is_huge_zero_pmd(*pmd)) {
+ /*
+ * FIXME: Do we want to invalidate secondary mmu by calling
+ * mmu_notifier_invalidate_range() see comments below inside
+ * __split_huge_pmd() ?
+ *
+ * We are going from a zero huge page write protected to zero
+ * small page also write protected so it does not seems useful
+ * to invalidate secondary mmu at this time.
+ */
return __split_huge_zero_page_pmd(vma, haddr, pmd);
}
@@ -2234,7 +2258,21 @@ void __split_huge_pmd(struct vm_area_str
__split_huge_pmd_locked(vma, pmd, haddr, freeze);
out:
spin_unlock(ptl);
- mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
+ /*
+ * No need to double call mmu_notifier->invalidate_range() callback.
+ * They are 3 cases to consider inside __split_huge_pmd_locked():
+ * 1) pmdp_huge_clear_flush_notify() call invalidate_range() obvious
+ * 2) __split_huge_zero_page_pmd() read only zero page and any write
+ * fault will trigger a flush_notify before pointing to a new page
+ * (it is fine if the secondary mmu keeps pointing to the old zero
+ * page in the meantime)
+ * 3) Split a huge pmd into pte pointing to the same page. No need
+ * to invalidate secondary tlb entry they are all still valid.
+ * any further changes to individual pte will notify. So no need
+ * to call mmu_notifier->invalidate_range()
+ */
+ mmu_notifier_invalidate_range_only_end(mm, haddr, haddr +
+ HPAGE_PMD_SIZE);
}
void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
diff -puN mm/memory.c~mm-mmu_notifier-avoid-call-to-invalidate_range-in-range_end mm/memory.c
--- a/mm/memory.c~mm-mmu_notifier-avoid-call-to-invalidate_range-in-range_end
+++ a/mm/memory.c
@@ -2554,7 +2554,11 @@ static int wp_page_copy(struct vm_fault
put_page(new_page);
pte_unmap_unlock(vmf->pte, vmf->ptl);
- mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+ /*
+ * No need to double call mmu_notifier->invalidate_range() callback as
+ * the above ptep_clear_flush_notify() did already call it.
+ */
+ mmu_notifier_invalidate_range_only_end(mm, mmun_start, mmun_end);
if (old_page) {
/*
* Don't let another task, with possibly unlocked vma,
diff -puN mm/migrate.c~mm-mmu_notifier-avoid-call-to-invalidate_range-in-range_end mm/migrate.c
--- a/mm/migrate.c~mm-mmu_notifier-avoid-call-to-invalidate_range-in-range_end
+++ a/mm/migrate.c
@@ -2089,7 +2089,11 @@ int migrate_misplaced_transhuge_page(str
set_page_owner_migrate_reason(new_page, MR_NUMA_MISPLACED);
spin_unlock(ptl);
- mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+ /*
+ * No need to double call mmu_notifier->invalidate_range() callback as
+ * the above pmdp_huge_clear_flush_notify() did already call it.
+ */
+ mmu_notifier_invalidate_range_only_end(mm, mmun_start, mmun_end);
/* Take an "isolate" reference and put new page on the LRU. */
get_page(new_page);
@@ -2805,9 +2809,14 @@ static void migrate_vma_pages(struct mig
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
}
+ /*
+ * No need to double call mmu_notifier->invalidate_range() callback as
+ * the above ptep_clear_flush_notify() inside migrate_vma_insert_page()
+ * did already call it.
+ */
if (notified)
- mmu_notifier_invalidate_range_end(mm, mmu_start,
- migrate->end);
+ mmu_notifier_invalidate_range_only_end(mm, mmu_start,
+ migrate->end);
}
/*
diff -puN mm/mmu_notifier.c~mm-mmu_notifier-avoid-call-to-invalidate_range-in-range_end mm/mmu_notifier.c
--- a/mm/mmu_notifier.c~mm-mmu_notifier-avoid-call-to-invalidate_range-in-range_end
+++ a/mm/mmu_notifier.c
@@ -190,7 +190,9 @@ void __mmu_notifier_invalidate_range_sta
EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
- unsigned long start, unsigned long end)
+ unsigned long start,
+ unsigned long end,
+ bool only_end)
{
struct mmu_notifier *mn;
int id;
@@ -204,8 +206,13 @@ void __mmu_notifier_invalidate_range_end
* subsystem registers either invalidate_range_start()/end() or
* invalidate_range(), so this will be no additional overhead
* (besides the pointer check).
+ *
+ * We skip call to invalidate_range() if we know it is safe ie
+ * call site use mmu_notifier_invalidate_range_only_end() which
+ * is safe to do when we know that a call to invalidate_range()
+ * already happen under page table lock.
*/
- if (mn->ops->invalidate_range)
+ if (!only_end && mn->ops->invalidate_range)
mn->ops->invalidate_range(mn, mm, start, end);
if (mn->ops->invalidate_range_end)
mn->ops->invalidate_range_end(mn, mm, start, end);
_
--
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