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

[John Hubbard <jhubbard@nvidia.com>]

On 2/14/22 12:00, Matthew Wilcox (Oracle) wrote:
> invalidate_inode_page() is the only caller of invalidate_complete_page()
> and inlining it reveals that the first check is unnecessary (because we
> hold the page locked, and we just retrieved the mapping from the page).

I just noticed this yesterday, when reviewing Rik's page poisoning fix.
I had a patch for it squirreled away, but I missed the point about
removing that extraneous mapping check. Glad you spotted it.

...
> @@ -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.
  */


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

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

Either way, looks good:

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
-- 
John Hubbard
NVIDIA

>   		return 0;
>   	if (page_mapped(page))
>   		return 0;
> -	return invalidate_complete_page(mapping, page);
> +	if (page_has_private(page) && !try_to_release_page(page, 0))
> +		return 0;
> +
> +	return remove_mapping(mapping, page);
>   }
>   
>   /**
> @@ -584,7 +566,7 @@ void invalidate_mapping_pagevec(struct address_space *mapping,
>   }
>   
>   /*
> - * This is like invalidate_complete_page(), except it ignores the page's
> + * This is like invalidate_inode_page(), except it ignores the page's
>    * refcount.  We do this because invalidate_inode_pages2() needs stronger
>    * invalidation guarantees, and cannot afford to leave pages behind because
>    * shrink_page_list() has a temp ref on them, or because they're transiently