Re: [PATCH 04/10] mm/truncate: Replace page_mapped() call in invalidate_inode_page()

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On Mon, Feb 14, 2022 at 08:00:11PM +0000, Matthew Wilcox (Oracle) wrote:
> folio_mapped() is expensive because it has to check each page's mapcount
> field.  A cheaper check is whether there are any extra references to
> the page, other than the one we own and the ones held by the page cache.
> The call to remove_mapping() will fail in any case if it cannot freeze
> the refcount, but failing here avoids cycling the i_pages spinlock.

This is the patch that's causing ltp's readahead02 test to break.
Haven't dug into why yet, but it happens without large folios, so
I got something wrong.

> diff --git a/mm/truncate.c b/mm/truncate.c
> index b73c30c95cd0..d67fa8871b75 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -287,7 +287,7 @@ int invalidate_inode_page(struct page *page)
>  		return 0;
>  	if (folio_test_dirty(folio) || folio_test_writeback(folio))
>  		return 0;
> -	if (page_mapped(page))
> +	if (folio_ref_count(folio) > folio_nr_pages(folio) + 1)
>  		return 0;
>  	if (folio_has_private(folio) && !filemap_release_folio(folio, 0))
>  		return 0;
> -- 
> 2.34.1
> 




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