Re: [PATCH 03/14] net: tcp_memcontrol: properly detect ancestor socket pressure

From: Johannes Weiner
Date: Sat Nov 14 2015 - 10:15:36 EST

On Sat, Nov 14, 2015 at 03:45:52PM +0300, Vladimir Davydov wrote:
> On Thu, Nov 12, 2015 at 06:41:22PM -0500, Johannes Weiner wrote:
> > When charging socket memory, the code currently checks only the local
> > page counter for excess to determine whether the memcg is under socket
> > pressure. But even if the local counter is fine, one of the ancestors
> > could have breached its limit, which should also force this child to
> > enter socket pressure. This currently doesn't happen.
> >
> > Fix this by using page_counter_try_charge() first. If that fails, it
> > means that either the local counter or one of the ancestors are in
> > excess of their limit, and the child should enter socket pressure.
> >
> > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Reviewed-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>

Thanks Vladimir!

> For the record: it was broken by commit 3e32cb2e0a12 ("mm: memcontrol:
> lockless page counters").

I didn't realize that.

Fixes: 3e32cb2e0a12 ("mm: memcontrol: lockless page counters")
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