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SubjectRe: [PATCH] mm: remove useless rcu lock-unlock from mapping_tagged()
On Sun, Jul 17, 2011 at 03:35:23PM +0400, Konstantin Khlebnikov wrote:
> radix_tree_tagged() is lockless, it does not require any protection.

Indeed. The radix_tree_root structure is a field in the address_space
structure, so no protection is required to get at the field. If
protection is required on the mapping pointer itself, that would have
to happen in writeback_single_inode() and friends.

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
> ---
> mm/page-writeback.c | 6 +-----
> 1 files changed, 1 insertions(+), 5 deletions(-)
>
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 31f6988..919b45e 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1405,10 +1405,6 @@ EXPORT_SYMBOL(test_set_page_writeback);
> */
> int mapping_tagged(struct address_space *mapping, int tag)
> {
> - int ret;
> - rcu_read_lock();
> - ret = radix_tree_tagged(&mapping->page_tree, tag);
> - rcu_read_unlock();
> - return ret;
> + return radix_tree_tagged(&mapping->page_tree, tag);
> }
> EXPORT_SYMBOL(mapping_tagged);
>
> --
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