Re: [PATCH v2 1/5] mm, memcg: reduce size of struct mem_cgroup by using bit field

From: Yafang Shao <laoar.shao@gmail.com>
To: Roman Gushchin <guro@fb.com>
Cc: "hannes@cmpxchg.org" <hannes@cmpxchg.org>,
	"david@fromorbit.com" <david@fromorbit.com>,
	"mhocko@kernel.org" <mhocko@kernel.org>,
	"vdavydov.dev@gmail.com" <vdavydov.dev@gmail.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v2 1/5] mm, memcg: reduce size of struct mem_cgroup by using bit field
Date: Fri, 27 Dec 2019 09:03:27 +0800	[thread overview]
Message-ID: <CALOAHbCQ=9dpKBjfbWv8hyU_D4Xiv5oDHFE4Ofuv57a6boo+iA@mail.gmail.com> (raw)
In-Reply-To: <20191226212320.GA22734@tower.dhcp.thefacebook.com>

On Fri, Dec 27, 2019 at 5:23 AM Roman Gushchin <guro@fb.com> wrote:
>
> On Tue, Dec 24, 2019 at 02:53:22AM -0500, Yafang Shao wrote:
> > There are some members in struct mem_group can be either 0(false) or
> > 1(true), so we can define them using bit field to reduce size. With this
> > patch, the size of struct mem_cgroup can be reduced by 64 bytes in theory,
> > but as there're some MEMCG_PADDING()s, the real number may be different,
> > which is relate with the cacheline size. Anyway, this patch could reduce
> > the size of struct mem_cgroup more or less.
>
> It seems it's not really related to the rest of the patchset, isn't it?
>

Right.

> Can you, please, post it separately?
>

Sure. Will post it separately.

> Also, I'd move the tcp-related stuff up, so that all oom-related fields
> would be together.

OK. Thanks for your comment.

> Otherwise lgtm.
>
> Thanks!
>
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> >  include/linux/memcontrol.h | 21 ++++++++++++---------
> >  1 file changed, 12 insertions(+), 9 deletions(-)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index a7a0a1a5..612a457 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -229,20 +229,26 @@ struct mem_cgroup {
> >       /*
> >        * Should the accounting and control be hierarchical, per subtree?
> >        */
> > -     bool use_hierarchy;
> > +     unsigned int use_hierarchy : 1;
> >
> >       /*
> >        * Should the OOM killer kill all belonging tasks, had it kill one?
> >        */
> > -     bool oom_group;
> > +     unsigned int  oom_group : 1;
> >
> >       /* protected by memcg_oom_lock */
> > -     bool            oom_lock;
> > -     int             under_oom;
> > +     unsigned int oom_lock : 1;
> >
> > -     int     swappiness;
> >       /* OOM-Killer disable */
> > -     int             oom_kill_disable;
> > +     unsigned int oom_kill_disable : 1;
> > +
> > +     /* Legacy tcp memory accounting */
> > +     unsigned int tcpmem_active : 1;
> > +     unsigned int tcpmem_pressure : 1;
> > +
> > +     int under_oom;
> > +
> > +     int     swappiness;
> >
> >       /* memory.events and memory.events.local */
> >       struct cgroup_file events_file;
> > @@ -297,9 +303,6 @@ struct mem_cgroup {
> >
> >       unsigned long           socket_pressure;
> >
> > -     /* Legacy tcp memory accounting */
> > -     bool                    tcpmem_active;
> > -     int                     tcpmem_pressure;
> >
> >  #ifdef CONFIG_MEMCG_KMEM
> >          /* Index in the kmem_cache->memcg_params.memcg_caches array */
> > --
> > 1.8.3.1
> >
> >