Re: [PATCH] kpageflags: respect folio head-page flag placement

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Wed, Oct 25, 2023 at 04:12:37PM -0400, Gregory Price wrote:
> +++ b/fs/proc/page.c
> @@ -188,20 +188,31 @@ u64 stable_page_flags(struct page *page)
>  		u |= 1 << KPF_SLAB;
>  
>  	u |= kpf_copy_bit(k, KPF_ERROR,		PG_error);
> -	u |= kpf_copy_bit(k, KPF_DIRTY,		PG_dirty);
> +
> +	if (PageDirty(page))
> +		u |= 1 << KPF_DIRTY;

This is not the way to do it.

At the beginning of the function, add:

	struct folio *folio = page_folio(page);

Then use folio_test_XXX istead of PageXXX().