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

Michal Hocko
2016-08-02T13:03:42Z

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@virtuozzo.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@suse.com>
>
> Thanks!
>
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--
Michal Hocko
SUSE Labs