linux-kernel - Re: [PATCH v2 07/15] mm, swap: tidy up swap device and cluster info helpers

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Message-ID: <84d3ab47-a960-4709-b127-ffbb8d85ac23@redhat.com>
Date: Mon, 8 Sep 2025 14:21:16 +0200
From: David Hildenbrand <david@...hat.com>
To: Kairui Song <kasong@...cent.com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Matthew Wilcox <willy@...radead.org>, Hugh Dickins <hughd@...gle.com>,
 Chris Li <chrisl@...nel.org>, Barry Song <baohua@...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>, Yosry Ahmed <yosryahmed@...gle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 07/15] mm, swap: tidy up swap device and cluster info
 helpers

On 05.09.25 21:13, Kairui Song 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

"Tidy this up and improve the function names." ?

> swap entry/type is valid and the device is pinned, use the new introduced
> __swap_entry_to_info/__swap_type_to_info instead. They have more debug
> sanity checks and lower overhead as they are inlined.
> 
> Callers that may expect a NULL value should use
> swap_entry_to_info/swap_type_to_info instead.
> 
> No feature change. The rearranged codes should have had no effect, or
> they should have been hitting NULL de-ref bugs already. Only some new
> sanity checks are added so potential issues may show up in debug build.
> 
> The new helpers will be frequently used with swap table later when working
> with swap cache folios. A locked swap cache folio ensures the entries are
> valid and stable so these helpers are very helpful.
> 
> Signed-off-by: Kairui Song <kasong@...cent.com>
> Acked-by: Chris Li <chrisl@...nel.org>
> Reviewed-by: Barry Song <baohua@...nel.org>
> ---

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers

David / dhildenb