linux-kernel - Re: [v2 PATCH] move_pages.2: Returning positive value is a new error case

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Date:   Thu, 30 Jan 2020 13:02:53 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, mtk.manpages@...il.com,
        akpm@...ux-foundation.org, linux-man@...r.kernel.org,
        linux-api@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH] move_pages.2: Returning positive value is a new error
 case

On Thu 30-01-20 10:06:28, Vlastimil Babka wrote:
> On 1/29/20 10:48 PM, Yang Shi wrote:
> > Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"),
> > the semantic of move_pages() has changed to return the number of
> > non-migrated pages if they were result of a non-fatal reasons (usually a
> > busy page).  This was an unintentional change that hasn't been noticed
> > except for LTP tests which checked for the documented behavior.
> > 
> > There are two ways to go around this change.  We can even get back to the
> > original behavior and return -EAGAIN whenever migrate_pages is not able
> 
> The manpage says EBUSY, not EAGAIN? And should its description be
> updated too?

The idea was that we _could_ return EAGAIN from the syscall if
migrate_pages > 0.

> I.e. that it's no longer returned since 4.17?

I am pretty sure this will require a deeper consideration. Do we return
EIO/EINVAL?
-- 
Michal Hocko
SUSE Labs