mm: accelerate mm_populate() treatment of THP pages

This change adds a follow_page_mask function which is equivalent to
follow_page, but with an extra page_mask argument.

follow_page_mask sets *page_mask to HPAGE_PMD_NR - 1 when it encounters
a THP page, and to 0 in other cases.

__get_user_pages() makes use of this in order to accelerate populating
THP ranges - that is, when both the pages and vmas arrays are NULL, we
don't need to iterate HPAGE_PMD_NR times to cover a single THP page (and
we also avoid taking mm->page_table_lock that many times).

Signed-off-by: Michel Lespinasse <walken@google.com>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 27 insertions, 10 deletions

diff --git a/mm/memory.c b/mm/memory.c
index bc929dbad215..5d2ef1217d0c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1462,10 +1462,11 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
 EXPORT_SYMBOL_GPL(zap_vma_ptes);
 
 /**
- * follow_page - look up a page descriptor from a user-virtual address
+ * follow_page_mask - look up a page descriptor from a user-virtual address
  * @vma: vm_area_struct mapping @address
  * @address: virtual address to look up
  * @flags: flags modifying lookup behaviour
+ * @page_mask: on output, *page_mask is set according to the size of the page
  *
  * @flags can have FOLL_ flags set, defined in <linux/mm.h>
  *
@@ -1473,8 +1474,9 @@ EXPORT_SYMBOL_GPL(zap_vma_ptes);
  * an error pointer if there is a mapping to something not represented
  * by a page descriptor (see also vm_normal_page()).
  */
-struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
-                        unsigned int flags)
+struct page *follow_page_mask(struct vm_area_struct *vma,
+                              unsigned long address, unsigned int flags,
+                              unsigned int *page_mask)
 {
         pgd_t *pgd;
         pud_t *pud;
@@ -1484,6 +1486,8 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
         struct page *page;
         struct mm_struct *mm = vma->vm_mm;
 
+        *page_mask = 0;
+
         page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
         if (!IS_ERR(page)) {
                 BUG_ON(flags & FOLL_GET);
@@ -1530,6 +1534,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
                                 page = follow_trans_huge_pmd(vma, address,
                                                              pmd, flags);
                                 spin_unlock(&mm->page_table_lock);
+                                *page_mask = HPAGE_PMD_NR - 1;
                                 goto out;
                         }
                 } else
@@ -1684,6 +1689,7 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 {
         long i;
         unsigned long vm_flags;
+        unsigned int page_mask;
 
         if (!nr_pages)
                 return 0;
@@ -1761,6 +1767,7 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                                 get_page(page);
                         }
                         pte_unmap(pte);
+                        page_mask = 0;
                         goto next_page;
                 }
 
@@ -1778,6 +1785,7 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                 do {
                         struct page *page;
                         unsigned int foll_flags = gup_flags;
+                        unsigned int page_increm;
 
                         /*
                          * If we have a pending SIGKILL, don't keep faulting
@@ -1787,7 +1795,8 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                                 return i ? i : -ERESTARTSYS;
 
                         cond_resched();
-                        while (!(page = follow_page(vma, start, foll_flags))) {
+                        while (!(page = follow_page_mask(vma, start,
+                                                foll_flags, &page_mask))) {
                                 int ret;
                                 unsigned int fault_flags = 0;
 
@@ -1861,13 +1870,19 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 
                                 flush_anon_page(vma, page, start);
                                 flush_dcache_page(page);
+                                page_mask = 0;
                         }
 next_page:
-                        if (vmas)
+                        if (vmas) {
                                 vmas[i] = vma;
-                        i++;
-                        start += PAGE_SIZE;
-                        nr_pages--;
+                                page_mask = 0;
+                        }
+                        page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
+                        if (page_increm > nr_pages)
+                                page_increm = nr_pages;
+                        i += page_increm;
+                        start += page_increm * PAGE_SIZE;
+                        nr_pages -= page_increm;
                 } while (nr_pages && start < vma->vm_end);
         } while (nr_pages);
         return i;
diff --git a/mm/nommu.c b/mm/nommu.c
index 6ab706608492..da0d210fd403 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1819,9 +1819,11 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
         return ret;
 }
 
-struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
-                        unsigned int foll_flags)
+struct page *follow_page_mask(struct vm_area_struct *vma,
+                              unsigned long address, unsigned int flags,
+                              unsigned int *page_mask)
 {
+        *page_mask = 0;
         return NULL;
 }