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authorRik van Riel <riel@redhat.com>2014-04-07 15:36:57 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-04-07 16:35:50 -0700
commita5338093bfb462256f70f3450c08f73e59543e26 (patch)
tree52225510cc303cede1bff15405a0b66b378240df /mm/mprotect.c
parent1ad9f620c3a22fa800489455ce517c29e576934e (diff)
downloadlwn-a5338093bfb462256f70f3450c08f73e59543e26.tar.gz
lwn-a5338093bfb462256f70f3450c08f73e59543e26.zip
mm: move mmu notifier call from change_protection to change_pmd_range
The NUMA scanning code can end up iterating over many gigabytes of unpopulated memory, especially in the case of a freshly started KVM guest with lots of memory. This results in the mmu notifier code being called even when there are no mapped pages in a virtual address range. The amount of time wasted can be enough to trigger soft lockup warnings with very large KVM guests. This patch moves the mmu notifier call to the pmd level, which represents 1GB areas of memory on x86-64. Furthermore, the mmu notifier code is only called from the address in the PMD where present mappings are first encountered. The hugetlbfs code is left alone for now; hugetlb mappings are not relocatable, and as such are left alone by the NUMA code, and should never trigger this problem to begin with. Signed-off-by: Rik van Riel <riel@redhat.com> Acked-by: David Rientjes <rientjes@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Reported-by: Xing Gang <gang.xing@hp.com> Tested-by: Chegu Vinod <chegu_vinod@hp.com> Cc: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mprotect.c')
-rw-r--r--mm/mprotect.c15
1 files changed, 12 insertions, 3 deletions
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 2c51c79c8a69..c43d557941f8 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -140,9 +140,11 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
pgprot_t newprot, int dirty_accountable, int prot_numa)
{
pmd_t *pmd;
+ struct mm_struct *mm = vma->vm_mm;
unsigned long next;
unsigned long pages = 0;
unsigned long nr_huge_updates = 0;
+ unsigned long mni_start = 0;
pmd = pmd_offset(pud, addr);
do {
@@ -151,6 +153,13 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
next = pmd_addr_end(addr, end);
if (!pmd_trans_huge(*pmd) && pmd_none_or_clear_bad(pmd))
continue;
+
+ /* invoke the mmu notifier if the pmd is populated */
+ if (!mni_start) {
+ mni_start = addr;
+ mmu_notifier_invalidate_range_start(mm, mni_start, end);
+ }
+
if (pmd_trans_huge(*pmd)) {
if (next - addr != HPAGE_PMD_SIZE)
split_huge_page_pmd(vma, addr, pmd);
@@ -175,6 +184,9 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
pages += this_pages;
} while (pmd++, addr = next, addr != end);
+ if (mni_start)
+ mmu_notifier_invalidate_range_end(mm, mni_start, end);
+
if (nr_huge_updates)
count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
return pages;
@@ -234,15 +246,12 @@ unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
unsigned long end, pgprot_t newprot,
int dirty_accountable, int prot_numa)
{
- struct mm_struct *mm = vma->vm_mm;
unsigned long pages;
- mmu_notifier_invalidate_range_start(mm, start, end);
if (is_vm_hugetlb_page(vma))
pages = hugetlb_change_protection(vma, start, end, newprot);
else
pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
- mmu_notifier_invalidate_range_end(mm, start, end);
return pages;
}