linux-kernel - Re: [v2 PATCH] mm: move_pages: return valid node id in status if the page is already on the target node

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Date:   Thu, 5 Dec 2019 18:17:28 +0000 (UTC)
From:   Christopher Lameter <cl@...ux.com>
To:     Qian Cai <cai@....pw>
cc:     Yang Shi <yang.shi@...ux.alibaba.com>, fabecassis@...dia.com,
        jhubbard@...dia.com, mhocko@...e.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: [v2 PATCH] mm: move_pages: return valid node id in status if
 the page is already on the target node

On Thu, 5 Dec 2019, Qian Cai wrote:

> > On Dec 5, 2019, at 12:39 PM, Yang Shi <yang.shi@...ux.alibaba.com> wrote:
> >
> > There are definitely a few inconsistencies, but I think the manpage is quite clear for this specific case, which says "status is an array of integers that return the status of each page. The array contains valid values only if move_pages() did not return an error." And, it looks kernel just misbehaved since 4.17 due to the fixes commit, so it sounds like a regression too.
>
> “Only if”  in strictly logical term does not necessarily mean it must contain valid values if move_pages() succeed.

The intended meaning is that valid values in the status array are provided
when the syscall succeeds and not otherwise. In the error case there may
be some valid values but since the operation may have aborted not all
values may have a value.