Re: [PATCH 02/10] mm/truncate: Inline invalidate_complete_page() into its one caller

[Matthew Wilcox <willy@infradead.org>]

On Mon, Feb 14, 2022 at 03:09:09PM -0800, John Hubbard wrote:
> > @@ -309,7 +288,10 @@ int invalidate_inode_page(struct page *page)
> 
> It would be nice to retain some of the original comments. May I suggest
> this (it has an additional paragraph) for an updated version of comments
> above invalidate_inode_page():
> 
> /*
>  * Safely invalidate one page from its pagecache mapping.
>  * It only drops clean, unused pages. The page must be locked.
>  *
>  * This function can be called at any time, and is not supposed to throw away
>  * dirty pages.  But pages can be marked dirty at any time too, so use
>  * remove_mapping(), which safely discards clean, unused pages.
>  *
>  * Returns 1 if the page is successfully invalidated, otherwise 0.
>  */

By the end of this series, it becomes:

/**
 * invalidate_inode_page() - Remove an unused page from the pagecache.
 * @page: The page to remove.
 *
 * Safely invalidate one page from its pagecache mapping.
 * It only drops clean, unused pages.
 *
 * Context: Page must be locked.
 * Return: The number of pages successfully removed.
 */

> Also, as long as you're there, a newline after the mapping declaration
> would bring this routine into compliance with that convention.

Again, by the end, we're at:

        struct folio *folio = page_folio(page);
        struct address_space *mapping = folio_mapping(folio);

        /* The page may have been truncated before it was locked */
        if (!mapping)
                return 0;
        return mapping_shrink_folio(mapping, folio);

> hmmm, now I wonder why this isn't a boolean function. And I think the
> reason is that it's quite old.

We could make this return a bool and have the one user that cares
call folio_nr_pages().  I don't have a strong preference.

> Either way, looks good:
> 
> Reviewed-by: John Hubbard <jhubbard@nvidia.com>

Thanks!