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

[Dave Chinner <david@xxxxxxxxxxxxx>]

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@xxxxxxxxxx>
....
> +             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@xxxxxxxxxxxxx