linux-kernel - Re: [v3 PATCH] mm: move_pages: return valid node id in status if the page is already on the target node

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Message-Id: <D04891DC-0EE8-4EA0-8541-97E4AB4DED3C@lca.pw>
Date:   Thu, 5 Dec 2019 17:23:44 -0500
From:   Qian Cai <cai@....pw>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     fabecassis@...dia.com, jhubbard@...dia.com, mhocko@...e.com,
        cl@...ux.com, vbabka@...e.cz, mgorman@...hsingularity.net,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [v3 PATCH] mm: move_pages: return valid node id in status if the page is already on the target node



> On Dec 5, 2019, at 5:09 PM, Yang Shi <yang.shi@...ux.alibaba.com> wrote:
> 
> As I said the status return value issue is a regression, but the -ENOENT issue has been there since the syscall was introduced (The visual inspection shows so I didn't actually run test against 2.6.x kernel, but it returns 0 for >= 3.10 at least). It does need further clarification (doc problem or code problem).

The question is why we should care about this change of behavior. It is arguably you are even trying to fix an ambiguous part of the manpage, but instead leave a more obviously one still broken. It is really difficult to understand the logical here.

> 
> Michal also noticed several inconsistencies when he was reworking move_pages(), and I agree with him that we'd better not touch them without a clear usecase.

It could argue that there is no use case to restore the behavior either.