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

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Date:	Tue, 2 Aug 2016 15:42:20 +0300
From:	Vladimir Davydov <vdavydov@...tuozzo.com>
To:	Michal Hocko <mhocko@...nel.org>
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, 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.

> 
> Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!