linux-kernel - Re: [PATCH v2 2/5] mmzone: Introduce folio

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Date:   Wed, 14 Jun 2023 13:13:05 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2 2/5] mmzone: Introduce folio_migratetype()

On Tue, 13 Jun 2023 19:13:09 -0700 "Vishal Moola (Oracle)" <vishal.moola@...il.com> wrote:

> Introduce folio_migratetype() as a folio equivalent for
> get_pageblock_migratetype(). This function intends to return the
> migratetype the folio is located in, hence the name choice.
> 
> ...
>
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -105,6 +105,9 @@ extern int page_group_by_mobility_disabled;
>  #define get_pageblock_migratetype(page)					\
>  	get_pfnblock_flags_mask(page, page_to_pfn(page), MIGRATETYPE_MASK)
>  
> +#define folio_migratetype(folio)				\
> +	get_pfnblock_flags_mask(&folio->page, folio_pfn(folio),		\
> +			MIGRATETYPE_MASK)

Theoretically this is risky because it evaluates its argument more than
once.  Although folio_migratetype(folio++) seems an unlikely thing to do.

An inlined C function is always preferable.  My quick attempt at that
reveals that the header files are All Messed Up As Usual.