Re: [PATCH v7 2/4] xfs: Introduce a helper routine to probe data or hole offset from page cache

[Dave Chinner <david@fromorbit.com>]

On Mon, Aug 13, 2012 at 09:07:58PM +0800, Jeff Liu wrote:
> helper routine to lookup data or hole offset from page cache for unwritten extents.
> 
> Signed-off-by: Jie Liu <jeff.liu@oracle.com>
....
> +		unsigned int	i;
> +
> +		want = min_t(pgoff_t, end - index, (pgoff_t)PAGEVEC_SIZE);

No need for the cast to (pgoff_t) here. That's what the min_t()
macro does for you.

> +		for (i = 0; i < nr_pages; i++) {
> +			struct page	*page = pvec.pages[i];
> +			loff_t		b_offset;
> +
> +			/*
> +			 * Page index is out of range, searching done.
> +			 * If the current offset is not reaches the end
> +			 * of the specified search range, there should
> +			 * be a hole between them.
> +			 */
> +			if (page->index > end) {
> +				if (type == HOLE_OFF && lastoff < endoff) {
> +					*offset = lastoff;
> +					found = true;
> +				}
> +				goto out;
> +			}
> +
> +			lock_page(page);
> +			/*
> +			 * Page truncated or invalidated(page->mapping == NULL).
> +			 * We can freely skip it and proceed to check the next
> +			 * page.
> +			 */
> +			if (unlikely(page->mapping != inode->i_mapping)) {
> +				unlock_page(page);
> +				continue;
> +			}

Still need to check page->index again after locking the page. As
this isn't performance critical, I don't think you need the check
before the page is locked, anyway....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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