Re: [RFC] Free up page->private for compound pages

[Hugh Dickins <hugh@veritas.com>]

On Wed, 4 Apr 2007, Christoph Lameter wrote:
> 
> V1->V2
> 	- Use alias to PG_reclaim
> 
> +static inline struct page *compound_head(struct page *page)
> +{
> +	if (unlikely(PageTail(page)))
> +		return page->first_page;
> +	return page;
> +}
> +
>  static inline int page_count(struct page *page)
>  {
> -	if (unlikely(PageCompound(page)))
> -		page = (struct page *)page_private(page);
> -	return atomic_read(&page->_count);
> +	return atomic_read(&compound_head(page)->_count);
>  }

No, you don't want anyone looking at the page_count of a page
currently under reclaim, or doing a get_page on it, to go veering
off through its page->private (page->first_page comes from another
of your patches, not in -mm).  Looks like you need to add a test for
PageCompound in compound_head (what a surprise!), unfortunately.

Hugh

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