On Thu, Jan 28, 2016 at 12:17 AM, Matthew Wilcox
<matthew.r.wilcox@xxxxxxxxx> wrote:
> From: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
>
> shmem likes to occasionally drop the lock, schedule, then reacqire
> the lock and continue with the iteration from the last place it
> left off. This is currently done with a pretty ugly goto. Introduce
> radix_tree_iter_next() and use it throughout shmem.c.
>
> Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
> ---
> include/linux/radix-tree.h | 15 +++++++++++++++
> mm/shmem.c | 12 +++---------
> 2 files changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
> index db0ed595749b..dec2c6c77eea 100644
> --- a/include/linux/radix-tree.h
> +++ b/include/linux/radix-tree.h
> @@ -403,6 +403,21 @@ void **radix_tree_iter_retry(struct radix_tree_iter *iter)
> }
>
> /**
> + * radix_tree_iter_next - resume iterating when the chunk may be invalid
> + * @iter: iterator state
> + *
> + * If the iterator needs to release then reacquire a lock, the chunk may
> + * have been invalidated by an insertion or deletion. Call this function
> + * to continue the iteration from the next index.
> + */
> +static inline __must_check
> +void **radix_tree_iter_next(struct radix_tree_iter *iter)
> +{
> + iter->next_index = iter->index + 1;
> + return NULL;
> +}
> +
> +/**
This works for normal iterator but not for tagged.
It must also reset iter->tags to zero.
> * radix_tree_chunk_size - get current chunk size
> *
> * @iter: pointer to radix tree iterator
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 6ec14b70d82d..438ea8004c26 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -376,7 +376,6 @@ unsigned long shmem_partial_swap_usage(struct address_space *mapping,
>
> rcu_read_lock();
>
> -restart:
> radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
> if (iter.index >= end)
> break;
> @@ -398,8 +397,7 @@ restart:
>
> if (need_resched()) {
> cond_resched_rcu();
> - start = iter.index + 1;
> - goto restart;
> + slot = radix_tree_iter_next(&iter);
> }
> }
>
> @@ -1950,7 +1948,6 @@ static void shmem_tag_pins(struct address_space *mapping)
> start = 0;
> rcu_read_lock();
>
> -restart:
> radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
> page = radix_tree_deref_slot(slot);
> if (!page || radix_tree_exception(page)) {
> @@ -1967,8 +1964,7 @@ restart:
>
> if (need_resched()) {
> cond_resched_rcu();
> - start = iter.index + 1;
> - goto restart;
> + slot = radix_tree_iter_next(&iter);
> }
> }
> rcu_read_unlock();
> @@ -2005,7 +2001,6 @@ static int shmem_wait_for_pins(struct address_space *mapping)
>
> start = 0;
> rcu_read_lock();
> -restart:
> radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter,
> start, SHMEM_TAG_PINNED) {
>
> @@ -2039,8 +2034,7 @@ restart:
> continue_resched:
> if (need_resched()) {
> cond_resched_rcu();
> - start = iter.index + 1;
> - goto restart;
> + slot = radix_tree_iter_next(&iter);
> }
> }
> rcu_read_unlock();
> --
> 2.7.0.rc3
>
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