From: Nick Piggin Avoid down_write of the mmap_sem in madvise when we can help it. Acked-by: Hugh Dickins Signed-off-by: Nick Piggin Cc: Rik van Riel Signed-off-by: Andrew Morton --- mm/madvise.c | 33 +++++++++++++++++++++++++++++---- 1 files changed, 29 insertions(+), 4 deletions(-) diff -puN mm/madvise.c~mm-madvise-avoid-exclusive-mmap_sem mm/madvise.c --- a/mm/madvise.c~mm-madvise-avoid-exclusive-mmap_sem +++ a/mm/madvise.c @@ -12,6 +12,24 @@ #include /* + * Any behaviour which results in changes to the vma->vm_flags needs to + * take mmap_sem for writing. Others, which simply traverse vmas, need + * to only take it for reading. + */ +static int madvise_need_mmap_write(int behavior) +{ + switch (behavior) { + case MADV_REMOVE: + case MADV_WILLNEED: + case MADV_DONTNEED: + return 0; + default: + /* be safe, default to 1. list exceptions explicitly */ + return 1; + } +} + +/* * We can potentially split a vm area into separate * areas, each area with its own behavior. */ @@ -183,9 +201,9 @@ static long madvise_remove(struct vm_are + ((loff_t)vma->vm_pgoff << PAGE_SHIFT); /* vmtruncate_range needs to take i_mutex and i_alloc_sem */ - up_write(¤t->mm->mmap_sem); + up_read(¤t->mm->mmap_sem); error = vmtruncate_range(mapping->host, offset, endoff); - down_write(¤t->mm->mmap_sem); + down_read(¤t->mm->mmap_sem); return error; } @@ -270,7 +288,10 @@ asmlinkage long sys_madvise(unsigned lon int error = -EINVAL; size_t len; - down_write(¤t->mm->mmap_sem); + if (madvise_need_mmap_write(behavior)) + down_write(¤t->mm->mmap_sem); + else + down_read(¤t->mm->mmap_sem); if (start & ~PAGE_MASK) goto out; @@ -332,6 +353,10 @@ asmlinkage long sys_madvise(unsigned lon vma = find_vma(current->mm, start); } out: - up_write(¤t->mm->mmap_sem); + if (madvise_need_mmap_write(behavior)) + up_write(¤t->mm->mmap_sem); + else + up_read(¤t->mm->mmap_sem); + return error; } _