linux-kernel - Re: [PATCH] vmpressure: Fix subtree pressure detection

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Date:	Mon, 1 Feb 2016 22:32:36 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vmpressure: Fix subtree pressure detection

On Fri, 29 Jan 2016 11:37:49 +0300 Vladimir Davydov <vdavydov@...tuozzo.com> wrote:

> On Thu, Jan 28, 2016 at 08:24:30PM +0100, Vlastimil Babka wrote:
> > On 28.1.2016 16:55, Michal Hocko wrote:
> > > On Wed 27-01-16 19:28:57, Vladimir Davydov wrote:
> > >> When vmpressure is called for the entire subtree under pressure we
> > >> mistakenly use vmpressure->scanned instead of vmpressure->tree_scanned
> > >> when checking if vmpressure work is to be scheduled. This results in
> > >> suppressing all vmpressure events in the legacy cgroup hierarchy. Fix
> > >> it.
> > >>
> > >> Fixes: 8e8ae645249b ("mm: memcontrol: hook up vmpressure to socket pressure")
> > >> Signed-off-by: Vladimir Davydov <vdavydov@...tuozzo.com>
> > > 
> > > a = b += c made me scratch my head for a second but this looks correct
> > 
> > Ugh, it's actually a = b += a
> > 
> > While clever and compact, this will make scratch their head anyone looking at
> > the code in the future. Is it worth it?
> 
> I'm just trying to be consistend with the !tree case, where we do
> exactly the same.

I stared suspiciously at it for a while, decided to let it go. 
Possibly we can remove local `scanned' altogether.  No matter, someone
will clean it all up sometime.