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

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Message-ID: <39087ce8-6f6a-4998-95e4-813e265318d0@redhat.com>
Date: Tue, 2 Sep 2025 15:33:21 +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 4/9] mm, swap: tidy up swap device and cluster info
 helpers

On 22.08.25 21:20, 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.

Shorter != better. But yes, "swp_swap" was a mess.

> 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.

High-level comments:

1) I hate the "swp" vs. "swap". Is that a valuable distinction or could 
we just convert it to "swap" as we touch it?

You're converting swap_type_to_swap_info() to swp_type_to_swap_info(), 
and I am not sure if that is the right direction :)


2) Can we just call it "swap_entry" when we work on a swap entry and 
"swap_type" when we work on a swap type in the function name?

swp_info() is a rather bad function name.


3) I am not sure about "to" -> "get". "to" is much more readable in that 
context and consistent.


4) swp_info[] vs. swap_info() gah.


I would just have done:

swap_type_to_info(int type)
__swap_type_to_info(int type)
swap_entry_to_info(swp_entry_t entry)
__swap_entry_to_info(swp_entry_t entry)

__ are the expert functions where we don't expect NULL.

-- 
Cheers

David / dhildenb