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>

Author: walken-google

include/linux/mm.h

@@ -1629,8 +1629,17 @@ int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
 int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
 unsigned long pfn);
 
-struct page *follow_page(struct vm_area_struct *, unsigned long address,
-unsigned int foll_flags);
+struct page *follow_page_mask(struct vm_area_struct *vma,
+ unsigned long address, unsigned int foll_flags,
+ unsigned int *page_mask);
+
+static inline struct page *follow_page(struct vm_area_struct *vma,
+unsigned long address, unsigned int foll_flags)
+{
+unsigned int unused_page_mask;
+return follow_page_mask(vma, address, foll_flags, &unused_page_mask);
+}
+
 #define FOLL_WRITE0x01/* check pte is writable */
 #define FOLL_TOUCH0x02/* mark page accessed */
 #define FOLL_GET0x04/* do get_page on page */

mm/memory.c

@@ -1462,19 +1462,21 @@ 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>
  *
  * Returns the mapped (struct page *), %NULL if no mapping exists, or
  * 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;

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;
 }