Re: [Patch] rcu: remove dead code in include/linux/pagemap.h

Paul E. McKenney
2011-01-31T07:40:29Z

On Mon, Jan 31, 2011 at 02:27:04PM +0800, Amerigo Wang wrote:
> TREE_RCU depends on !PREEMPT && SMP, when !CONFIG_SMP is true, CONFIG_TREE_RCU
> will be false, thus "!defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)"
> is always false.

The relationship between these configuration parameters has indeed
changed. But I am wondering if rather than removing these, the
conditions need to be updated as shown below.

Thanx, Paul

> Remove these dead code.
>
> Signed-off-by: WANG Cong <amwang@redhat.com>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>
> ---
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 9c66e99..e2bbbe3 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -133,23 +133,6 @@ static inline int page_cache_get_speculative(struct page *page)
> {
> VM_BUG_ON(in_interrupt());
>
> -#if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)

#if !defined(CONFIG_SMP) && defined(CONFIG_TREE_PREEMPT_RCU)

/* Must have CONFIG_PREEMPT here, implied by CONFIG_TREE_PREEMPT_RCU. */

> -# ifdef CONFIG_PREEMPT
VM_BUG_ON(!in_atomic());
> -# endif
/*
* Preempt must be disabled here - we rely on rcu_read_lock doing
* this for us.
*
* Pagecache won't be truncated from interrupt context, so if we have
* found a page in the radix tree here, we have pinned its refcount by
* disabling preempt, and hence no need for the "speculative get" that
* SMP requires.
*/
VM_BUG_ON(page_count(page) == 0);
atomic_inc(&page->_count);

#else
if (unlikely(!get_page_unless_zero(page))) {
/*
* Either the page has been freed, or will be freed.
> @@ -158,7 +141,6 @@ static inline int page_cache_get_speculative(struct page *page)
*/
return 0;
}
#endif
> VM_BUG_ON(PageTail(page));
>
> return 1;
> @@ -171,17 +153,9 @@ static inline int page_cache_add_speculative(struct page *page, int count)
> {
> VM_BUG_ON(in_interrupt());
>
> -#if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
> -# ifdef CONFIG_PREEMPT
> - VM_BUG_ON(!in_atomic());
> -# endif
> - VM_BUG_ON(page_count(page) == 0);
> - atomic_add(count, &page->_count);
> -
> -#else
> if (unlikely(!atomic_add_unless(&page->_count, count, 0)))
> return 0;
> -#endif
> +
> VM_BUG_ON(PageCompound(page) && page != compound_head(page));
>
> return 1;
> --
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