mm: Count the number of pages affected in change_protection()

This will be used for three kinds of purposes:

 - to optimize mprotect()

 - to speed up working set scanning for working set areas that
   have not been touched

 - to more accurately scan per real working set

No change in functionality from this patch.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 52 insertions, 16 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 59a0059b39e2..712895eda0d0 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3014,7 +3014,7 @@ same_page:
         return i ? i : -EFAULT;
 }
 
-void hugetlb_change_protection(struct vm_area_struct *vma,
+unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
                 unsigned long address, unsigned long end, pgprot_t newprot)
 {
         struct mm_struct *mm = vma->vm_mm;
@@ -3022,6 +3022,7 @@ void hugetlb_change_protection(struct vm_area_struct *vma,
         pte_t *ptep;
         pte_t pte;
         struct hstate *h = hstate_vma(vma);
+        unsigned long pages = 0;
 
         BUG_ON(address >= end);
         flush_cache_range(vma, address, end);
@@ -3032,12 +3033,15 @@ void hugetlb_change_protection(struct vm_area_struct *vma,
                 ptep = huge_pte_offset(mm, address);
                 if (!ptep)
                         continue;
-                if (huge_pmd_unshare(mm, &address, ptep))
+                if (huge_pmd_unshare(mm, &address, ptep)) {
+                        pages++;
                         continue;
+                }
                 if (!huge_pte_none(huge_ptep_get(ptep))) {
                         pte = huge_ptep_get_and_clear(mm, address, ptep);
                         pte = pte_mkhuge(pte_modify(pte, newprot));
                         set_huge_pte_at(mm, address, ptep, pte);
+                        pages++;
                 }
         }
         spin_unlock(&mm->page_table_lock);
@@ -3049,6 +3053,8 @@ void hugetlb_change_protection(struct vm_area_struct *vma,
          */
         flush_tlb_range(vma, start, end);
         mutex_unlock(&vma->vm_file->f_mapping->i_mmap_mutex);
+
+        return pages << h->order;
 }
 
 int hugetlb_reserve_pages(struct inode *inode,
diff --git a/mm/mprotect.c b/mm/mprotect.c
index a40992610ab6..1e265be25f85 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -35,12 +35,13 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
 }
 #endif
 
-static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
+static unsigned long change_pte_range(struct mm_struct *mm, pmd_t *pmd,
                 unsigned long addr, unsigned long end, pgprot_t newprot,
                 int dirty_accountable)
 {
         pte_t *pte, oldpte;
         spinlock_t *ptl;
+        unsigned long pages = 0;
 
         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
         arch_enter_lazy_mmu_mode();
@@ -60,6 +61,7 @@ static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
                                 ptent = pte_mkwrite(ptent);
 
                         ptep_modify_prot_commit(mm, addr, pte, ptent);
+                        pages++;
                 } else if (IS_ENABLED(CONFIG_MIGRATION) && !pte_file(oldpte)) {
                         swp_entry_t entry = pte_to_swp_entry(oldpte);
 
@@ -72,18 +74,22 @@ static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
                                 set_pte_at(mm, addr, pte,
                                         swp_entry_to_pte(entry));
                         }
+                        pages++;
                 }
         } while (pte++, addr += PAGE_SIZE, addr != end);
         arch_leave_lazy_mmu_mode();
         pte_unmap_unlock(pte - 1, ptl);
+
+        return pages;
 }
 
-static inline void change_pmd_range(struct vm_area_struct *vma, pud_t *pud,
+static inline unsigned long change_pmd_range(struct vm_area_struct *vma, pud_t *pud,
                 unsigned long addr, unsigned long end, pgprot_t newprot,
                 int dirty_accountable)
 {
         pmd_t *pmd;
         unsigned long next;
+        unsigned long pages = 0;
 
         pmd = pmd_offset(pud, addr);
         do {
@@ -91,35 +97,42 @@ static inline void change_pmd_range(struct vm_area_struct *vma, pud_t *pud,
                 if (pmd_trans_huge(*pmd)) {
                         if (next - addr != HPAGE_PMD_SIZE)
                                 split_huge_page_pmd(vma->vm_mm, pmd);
-                        else if (change_huge_pmd(vma, pmd, addr, newprot))
+                        else if (change_huge_pmd(vma, pmd, addr, newprot)) {
+                                pages += HPAGE_PMD_NR;
                                 continue;
+                        }
                         /* fall through */
                 }
                 if (pmd_none_or_clear_bad(pmd))
                         continue;
-                change_pte_range(vma->vm_mm, pmd, addr, next, newprot,
+                pages += change_pte_range(vma->vm_mm, pmd, addr, next, newprot,
                                  dirty_accountable);
         } while (pmd++, addr = next, addr != end);
+
+        return pages;
 }
 
-static inline void change_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
+static inline unsigned long change_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
                 unsigned long addr, unsigned long end, pgprot_t newprot,
                 int dirty_accountable)
 {
         pud_t *pud;
         unsigned long next;
+        unsigned long pages = 0;
 
         pud = pud_offset(pgd, addr);
         do {
                 next = pud_addr_end(addr, end);
                 if (pud_none_or_clear_bad(pud))
                         continue;
-                change_pmd_range(vma, pud, addr, next, newprot,
+                pages += change_pmd_range(vma, pud, addr, next, newprot,
                                  dirty_accountable);
         } while (pud++, addr = next, addr != end);
+
+        return pages;
 }
 
-static void change_protection(struct vm_area_struct *vma,
+static unsigned long change_protection_range(struct vm_area_struct *vma,
                 unsigned long addr, unsigned long end, pgprot_t newprot,
                 int dirty_accountable)
 {
@@ -127,6 +140,7 @@ static void change_protection(struct vm_area_struct *vma,
         pgd_t *pgd;
         unsigned long next;
         unsigned long start = addr;
+        unsigned long pages = 0;
 
         BUG_ON(addr >= end);
         pgd = pgd_offset(mm, addr);
@@ -135,10 +149,30 @@ static void change_protection(struct vm_area_struct *vma,
                 next = pgd_addr_end(addr, end);
                 if (pgd_none_or_clear_bad(pgd))
                         continue;
-                change_pud_range(vma, pgd, addr, next, newprot,
+                pages += change_pud_range(vma, pgd, addr, next, newprot,
                                  dirty_accountable);
         } while (pgd++, addr = next, addr != end);
+
         flush_tlb_range(vma, start, end);
+
+        return pages;
+}
+
+unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
+                       unsigned long end, pgprot_t newprot,
+                       int dirty_accountable)
+{
+        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);
+        mmu_notifier_invalidate_range_end(mm, start, end);
+
+        return pages;
 }
 
 int
@@ -213,12 +247,8 @@ success:
                 dirty_accountable = 1;
         }
 
-        mmu_notifier_invalidate_range_start(mm, start, end);
-        if (is_vm_hugetlb_page(vma))
-                hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
-        else
-                change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
-        mmu_notifier_invalidate_range_end(mm, start, end);
+        change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
+
         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
         perf_event_mmap(vma);