[PATCH] mm: follow_page with inner ptlock

Final step in pushing down common core's page_table_lock.  follow_page no
longer wants caller to hold page_table_lock, uses pte_offset_map_lock itself;
and so no page_table_lock is taken in get_user_pages itself.

But get_user_pages (and get_futex_key) do then need follow_page to pin the
page for them: take Daniel's suggestion of bitflags to follow_page.

Need one for WRITE, another for TOUCH (it was the accessed flag before:
vanished along with check_user_page_readable, but surely get_numa_maps is
wrong to mark every page it finds as accessed), another for GET.

And another, ANON to dispose of untouched_anonymous_page: it seems silly for
that to descend a second time, let follow_page observe if there was no page
table and return ZERO_PAGE if so.  Fix minor bug in that: check VM_LOCKED -
make_pages_present ought to make readonly anonymous present.

Give get_numa_maps a cond_resched while we're there.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 1 insertions, 2 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 7e5e7ec2e36..d2fa42006d8 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -419,7 +419,6 @@ static struct numa_maps *get_numa_maps(const struct vm_area_struct *vma)
         for_each_node(i)
                 md->node[i] =0;
 
-        spin_lock(&mm->page_table_lock);
         for (vaddr = vma->vm_start; vaddr < vma->vm_end; vaddr += PAGE_SIZE) {
                 page = follow_page(mm, vaddr, 0);
                 if (page) {
@@ -434,8 +433,8 @@ static struct numa_maps *get_numa_maps(const struct vm_area_struct *vma)
                                 md->anon++;
                         md->node[page_to_nid(page)]++;
                 }
+                cond_resched();
         }
-        spin_unlock(&mm->page_table_lock);
         return md;
 }