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Subject: Re: [PATCH v6 01/27] mm: Introduce struct folio
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>, linux-mm@kvack.org
Cc:     linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-cachefs@redhat.com, linux-afs@lists.infradead.org
References: <20210331184728.1188084-1-willy@infradead.org>
 <20210331184728.1188084-2-willy@infradead.org>
From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
Message-ID: <f89f694f-d472-3287-51aa-86258e107361@rasmusvillemoes.dk>
Date:   Thu, 8 Apr 2021 11:01:57 +0200
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On 31/03/2021 20.47, Matthew Wilcox (Oracle) wrote:

> +static inline void folio_build_bug(void)
> +{
> +#define FOLIO_MATCH(pg, fl)						\
> +BUILD_BUG_ON(offsetof(struct page, pg) != offsetof(struct folio, fl));
> +
> +	FOLIO_MATCH(flags, flags);
> +	FOLIO_MATCH(lru, lru);
> +	FOLIO_MATCH(mapping, mapping);
> +	FOLIO_MATCH(index, index);
> +	FOLIO_MATCH(private, private);
> +	FOLIO_MATCH(_mapcount, _mapcount);
> +	FOLIO_MATCH(_refcount, _refcount);
> +#ifdef CONFIG_MEMCG
> +	FOLIO_MATCH(memcg_data, memcg_data);
> +#endif
> +#undef FOLIO_MATCH
> +	BUILD_BUG_ON(sizeof(struct page) != sizeof(struct folio));
> +}
> +

Perhaps do this next to the definition of struct folio instead of hiding
it in some arbitrary TU - hint, we have static_assert() that doesn't
need to be in function context. And consider amending FOLIO_MATCH by a
static_assert(__same_type(typeof_member(...), typeof_member(...))).

Rasmus