linux-kernel - Re: [PATCH 4/9] mm, swap: tidy up swap device and cluster info helpers

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Message-ID: <CAGsJ_4x8fgWchmf4C8EvVK+aSK7gZRKzp9h=z0V_RpD2TmXaOA@mail.gmail.com>
Date: Tue, 2 Sep 2025 14:02:11 +0800
From: Barry Song <21cnbao@...il.com>
To: Kairui Song <kasong@...cent.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, 
	Matthew Wilcox <willy@...radead.org>, Hugh Dickins <hughd@...gle.com>, Chris Li <chrisl@...nel.org>, 
	Baoquan He <bhe@...hat.com>, Nhat Pham <nphamcs@...il.com>, 
	Kemeng Shi <shikemeng@...weicloud.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	Ying Huang <ying.huang@...ux.alibaba.com>, Johannes Weiner <hannes@...xchg.org>, 
	David Hildenbrand <david@...hat.com>, Yosry Ahmed <yosryahmed@...gle.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/9] mm, swap: tidy up swap device and cluster info helpers

On Sat, Aug 23, 2025 at 3:21 AM Kairui Song <ryncsn@...il.com> wrote:
>
> From: Kairui Song <kasong@...cent.com>
>
> swp_swap_info is the most commonly used helper for retrieving swap info.
> It has an internal check that may lead to a NULL return value, but
> almost none of its caller checks the return value, making the internal
> check pointless. In fact, most of these callers already ensured the
> entry is valid and never expect a NULL value.
>
> Tidy this up and shorten the name. If the caller can make sure the
> swap entry/type is valid and the device is pinned, use the new introduced
> swp_info/swp_type_info instead. They have more debug sanity checks and
> lower overhead as they are inlined.
>
> Callers that may expect a NULL value should use
> swp_get_info/swp_type_get_info instead.
>
> No feature change. The rearranged codes should have had no effect, or
> they should have been hitting NULL de-ref bugs already. Some new sanity
> checks have been added to the debug build to catch potential misuse.
> And the new helpers will be used by swap cache when working with locked
> swap cache folios, as a locked swap cache ensures the entries are valid
> and stable.
>
> Signed-off-by: Kairui Song <kasong@...cent.com>

Reviewed-by: Barry Song <baohua@...nel.org>

Thanks
Barry