[PATCH 2/2] mm/mmu_notifier: avoid call to invalidate_range() in range_end()
jglisse at redhat.com
jglisse at redhat.com
Tue Oct 17 14:10:03 AEDT 2017
From: Jérôme Glisse <jglisse at redhat.com>
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
Signed-off-by: Jérôme Glisse <jglisse at redhat.com>
Cc: Andrea Arcangeli <aarcange at redhat.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Joerg Roedel <jroedel at suse.de>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit at amd.com>
Cc: David Woodhouse <dwmw2 at infradead.org>
Cc: Alistair Popple <alistair at popple.id.au>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Stephen Rothwell <sfr at canb.auug.org.au>
Cc: Andrew Donnellan <andrew.donnellan at au1.ibm.com>
Cc: iommu at lists.linux-foundation.org
Cc: linuxppc-dev at lists.ozlabs.org
---
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 --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 49c925c96b8a..6665c4624287 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -213,7 +213,8 @@ extern void __mmu_notifier_change_pte(struct mm_struct *mm,
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);
@@ -267,7 +268,14 @@ static inline void mmu_notifier_invalidate_range_end(struct mm_struct *mm,
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_invalidate_range_end(struct mm_struct *mm,
{
}
+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 --git a/mm/huge_memory.c b/mm/huge_memory.c
index ff5bc647b51d..b2912305994f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1220,7 +1220,12 @@ static int do_huge_pmd_wp_page_fallback(struct vm_fault *vmf, pmd_t orig_pmd,
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);
@@ -1369,7 +1374,12 @@ int do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
}
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:
@@ -2021,7 +2031,12 @@ void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud,
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 */
@@ -2096,6 +2111,15 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
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);
}
@@ -2231,7 +2255,21 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
__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 --git a/mm/memory.c b/mm/memory.c
index 47cdf4e85c2d..8a0c410037d2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2555,7 +2555,11 @@ static int wp_page_copy(struct vm_fault *vmf)
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 --git a/mm/migrate.c b/mm/migrate.c
index e00814ca390e..2f0f8190cb6f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2088,7 +2088,11 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
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);
@@ -2804,9 +2808,14 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
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 --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 314285284e6e..96edb33fd09a 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -190,7 +190,9 @@ void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
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(struct mm_struct *mm,
* 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);
--
2.13.6
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