linux-kernel - Re: [PATCH] radix-tree: account nodes to memcg only if explicitly requested

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Message-ID: <20160802124644.GL12403@dhcp22.suse.cz>
Date:	Tue, 2 Aug 2016 14:46:45 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] radix-tree: account nodes to memcg only if explicitly
 requested

On Tue 02-08-16 15:42:20, Vladimir Davydov wrote:
> On Tue, Aug 02, 2016 at 01:51:12PM +0200, Michal Hocko wrote:
> > On Mon 01-08-16 16:13:08, Vladimir Davydov wrote:
> > > Radix trees may be used not only for storing page cache pages, so
> > > unconditionally accounting radix tree nodes to the current memory cgroup
> > > is bad: if a radix tree node is used for storing data shared among
> > > different cgroups we risk pinning dead memory cgroups forever. So let's
> > > only account radix tree nodes if it was explicitly requested by passing
> > > __GFP_ACCOUNT to INIT_RADIX_TREE. Currently, we only want to account
> > > page cache entries, so mark mapping->page_tree so.
> > > 
> > > Signed-off-by: Vladimir Davydov <vdavydov@...tuozzo.com>
> > 
> > OK, the patch makes sense to me. Such a false sharing would be really
> > tedious to debug
> > 
> > Do we want to mark it for stable 4.6 to prevent from some pathological
> > issues. The patch is simple enough.
> 
> Makes sense, expecially taking into account that kmemcg is enabled by
> default now.
>
> I'll resend the patch for stable then.

Maybe Andrew just want's to mark it for stable with
Fixes: 58e698af4c63 ("radix-tree: account radix_tree_node to memory cgroup")
 Cc: stable # 4.6

> > Acked-by: Michal Hocko <mhocko@...e.com>
> 
> Thanks!
> 
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-- 
Michal Hocko
SUSE Labs