mm: unmap VM_PFNMAP mappings with optimized path

When unmapping VM_PFNMAP mappings, vm flags need to be updated.  Since the
vmas have been detached, so it sounds safe to update vm flags with read
mmap_sem.

Link: http://lkml.kernel.org/r/1537376621-51150-4-git-send-email-yang.shi@linux.alibaba.com
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index ea3188bcc9b46334831d267505976448e90df047..58e323c92c8e5ae498a1ad8efc778abb18419979 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2771,15 +2771,6 @@ static int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
                                munlock_vma_pages_all(tmp);
                        }
 
-                       /*
-                        * Unmapping vmas, which have VM_HUGETLB or VM_PFNMAP,
-                        * need get done with write mmap_sem held since they may
-                        * update vm_flags.
-                        */
-                       if (downgrade &&
-                           (tmp->vm_flags & VM_PFNMAP))
-                               downgrade = false;
-
                        tmp = tmp->vm_next;
                }
        }