linux-kernel - Re: [PATCH] mm: vmscan: Avoid signedness error for GCC 5.4

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Message-ID: <FF9F758FB6DEBA6B+668772f9-2604-4035-bb04-b59eabf9bbd3@uniontech.com>
Date: Wed, 7 May 2025 10:55:31 +0800
From: WangYuli <wangyuli@...ontech.com>
To: Matthew Wilcox <willy@...radead.org>, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, yuzhao@...gle.com,
 stevensd@...omium.org, kaleshsingh@...gle.com, zhanjun@...ontech.com,
 niecheng1@...ontech.com, guanwentao@...ontech.com
Subject: Re: [PATCH] mm: vmscan: Avoid signedness error for GCC 5.4

Hi Matthew Wilcox and Andrew Morton,

On 2025/5/7 00:22, Matthew Wilcox wrote:
> 1. This has nothing to do with the compiler version; the type-checking
> is built into min().

Thank you for pointing that out! My previous statement was incorrect.

The error is actually from the __types_ok check within the 
__careful_cmp_once macro failing, which triggered BUILD_BUG_ON.

But then, why do newer compilers compile this without error? Is it 
perhaps because they consider 4U - 1 to be signed?

> 2. We have min_t for a reason
Yes, using min_t instead of min is a better approach.
> 3. Why is a signed min the right answer instead of an unsigned min?
>
That is indeed false. Just as Andrew Morton said, "negative tier numbers 
are nonsensical".

Thank you for everyone's corrections. I'll submit a v2 patch.

-- 
WangYuli

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