From: Andrew Morton <akpm@linux-foundation.org>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linux MM <linux-mm@kvack.org>,
Pavel Emelyanov <xemul@parallels.com>
Subject: Re: [PATCH] mm: Don't forget to set softdirty on file mapped fault
Date: Tue, 8 Jul 2014 13:45:11 -0700 [thread overview]
Message-ID: <20140708134511.4a32b7400a952541a31e9078@linux-foundation.org> (raw)
In-Reply-To: <20140708204017.GG17860@moon.sw.swsoft.com>
On Wed, 9 Jul 2014 00:40:17 +0400 Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> On Tue, Jul 08, 2014 at 01:19:20PM -0700, Andrew Morton wrote:
> > On Tue, 8 Jul 2014 23:21:51 +0400 Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> >
> > > Otherwise we may not notice that pte was softdirty because pte_mksoft_dirty
> > > helper _returns_ new pte but not modifies argument.
> >
> > When fixing a bug, please describe the end-user visible effects of that
> > bug.
> >
> > [for the 12,000th time :(]
>
> "we may not notice that pte was softdirty" I thought it's enough, because
> that's the effect user sees -- pte is not dirtified where it should.
>
> Really sorry Andrew if I were not clear enough. What about: In case if page
> fault happend on dirty filemapping the newly created pte may not
> notice if old one were already softdirtified because pte_mksoft_dirty
> doesn't modify its argument but rather returns new pte value.
The user doesn't know or care about pte bits.
What actually *happens*? Does criu migration hang? Does it lose data?
Does it take longer?
IOW, what would an end-user's bug report look like?
It's important to think this way because a year from now some person
we've never heard of may be looking at a user's bug report and
wondering whether backporting this patch will fix it. Amongst other
reasons.
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next prev parent reply other threads:[~2014-07-08 20:45 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-08 19:21 Cyrill Gorcunov
2014-07-08 19:28 ` Pavel Emelyanov
2014-07-08 20:19 ` Andrew Morton
2014-07-08 20:40 ` Cyrill Gorcunov
2014-07-08 20:45 ` Andrew Morton [this message]
2014-07-08 20:54 ` Cyrill Gorcunov
2014-07-08 21:05 ` Andrew Morton
2014-07-08 21:15 ` Cyrill Gorcunov
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