mm: add FOLL_MLOCK follow_page flag.

Move the code to mlock pages from __mlock_vma_pages_range() to
follow_page().

This allows __mlock_vma_pages_range() to not have to break down work into
16-page batches.

An additional motivation for doing this within the present patch series is
that it'll make it easier for a later chagne to drop mmap_sem when
blocking on disk (we'd like to be able to resume at the page that was read
from disk instead of at the start of a 16-page batch).

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 60 deletions

diff --git a/mm/mlock.c b/mm/mlock.c
index 67b3dd8616dc..25cc9e88c540 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -159,10 +159,9 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
 {
         struct mm_struct *mm = vma->vm_mm;
         unsigned long addr = start;
-        struct page *pages[16]; /* 16 gives a reasonable batch */
         int nr_pages = (end - start) / PAGE_SIZE;
-        int ret = 0;
         int gup_flags;
+        int ret;
 
         VM_BUG_ON(start & ~PAGE_MASK);
         VM_BUG_ON(end   & ~PAGE_MASK);
@@ -170,7 +169,7 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
         VM_BUG_ON(end   > vma->vm_end);
         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
 
-        gup_flags = FOLL_TOUCH | FOLL_GET;
+        gup_flags = FOLL_TOUCH | FOLL_MLOCK;
         /*
          * We want to touch writable mappings with a write fault in order
          * to break COW, except for shared mappings because these don't COW
@@ -185,63 +184,9 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
                 nr_pages--;
         }
 
-        while (nr_pages > 0) {
-                int i;
-
-                cond_resched();
-
-                /*
-                 * get_user_pages makes pages present if we are
-                 * setting mlock. and this extra reference count will
-                 * disable migration of this page.  However, page may
-                 * still be truncated out from under us.
-                 */
-                ret = __get_user_pages(current, mm, addr,
-                                min_t(int, nr_pages, ARRAY_SIZE(pages)),
-                                gup_flags, pages, NULL);
-                /*
-                 * This can happen for, e.g., VM_NONLINEAR regions before
-                 * a page has been allocated and mapped at a given offset,
-                 * or for addresses that map beyond end of a file.
-                 * We'll mlock the pages if/when they get faulted in.
-                 */
-                if (ret < 0)
-                        break;
-
-                lru_add_drain();        /* push cached pages to LRU */
-
-                for (i = 0; i < ret; i++) {
-                        struct page *page = pages[i];
-
-                        if (page->mapping) {
-                                /*
-                                 * That preliminary check is mainly to avoid
-                                 * the pointless overhead of lock_page on the
-                                 * ZERO_PAGE: which might bounce very badly if
-                                 * there is contention.  However, we're still
-                                 * dirtying its cacheline with get/put_page:
-                                 * we'll add another __get_user_pages flag to
-                                 * avoid it if that case turns out to matter.
-                                 */
-                                lock_page(page);
-                                /*
-                                 * Because we lock page here and migration is
-                                 * blocked by the elevated reference, we need
-                                 * only check for file-cache page truncation.
-                                 */
-                                if (page->mapping)
-                                        mlock_vma_page(page);
-                                unlock_page(page);
-                        }
-                        put_page(page); /* ref from get_user_pages() */
-                }
-
-                addr += ret * PAGE_SIZE;
-                nr_pages -= ret;
-                ret = 0;
-        }
-
-        return ret;     /* 0 or negative error code */
+        ret = __get_user_pages(current, mm, addr, nr_pages, gup_flags,
+                               NULL, NULL);
+        return max(ret, 0);     /* 0 or negative error code */
 }
 
 /*