linux-kernel - Re: [PATCH] mm: fix the type of a parameter

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Message-Id: <20211201193408.49c88f8281d14fb2c61f9ee6@linux-foundation.org>
Date:   Wed, 1 Dec 2021 19:34:08 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Yixuan Cao <caoyixuan2019@...il.szu.edu.cn>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: fix the type of a parameter

On Thu,  2 Dec 2021 02:12:36 +0800 Yixuan Cao <caoyixuan2019@...il.szu.edu.cn> wrote:

> The type of "last_migrate_reason" in struct page_owner is short.
> However, the type of "reason" in the argument list of following functions
> __set_page_owner_migrate_reason
> set_page_owner_migrate_reason
> 
> is int, which is inconsistent.

Well.

I'd say "no", because `int' is a natural type and the packing of that
scalar into a `short' is an expedient little space-saving hack (ie, an
"implementation detail") which should be hidden from callers rather
than propagated back up the call stack.

However, all these `int's should be of type `enum migrate_reason'.  And
the lowest-level hack of stuffing that enum into a `short' should
remain an implementation detail, hidden from callers.