linux-kernel - Re: [PATCH 0/3] add folio

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Message-ID: <Y7h0xNGlj0qzFlua@casper.infradead.org>
Date:   Fri, 6 Jan 2023 19:21:40 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     SeongJae Park <sj@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Xiubo Li <xiubli@...hat.com>,
        Ilya Dryomov <idryomov@...il.com>,
        Jeff Layton <jlayton@...nel.org>, linux-mm@...ck.org,
        ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] add folio_headpage() macro

On Fri, Jan 06, 2023 at 05:40:25PM +0000, SeongJae Park wrote:
> The standard idiom for getting head page of a given folio is
> '&folio->page'.  It is efficient and safe even if the folio is NULL,
> because the offset of page field in folio is zero.  However, it makes
> the code not that easy to understand at the first glance, especially the
> NULL safety.  Also, sometimes people forget the idiom and use
> 'folio_page(folio, 0)' instead.  To make it easier to read and remember,
> add a new macro function called 'folio_headpage()' with the NULL case
> explanation.  Then, replace the 'folio_page(folio, 0)' calls with
> 'folio_headpage(folio)'.

No.  Everywhere that uses &folio->page is a place that needs to be fixed.
It shouldn't have a nice convenience macro.  It should make you mildly
uncomfortable.