On Tue, 3 Aug 2010 13:31:09 +0900
Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote:
> Hi.
>
> Thank you for all of your works.
>
> Several comments are inlined.
>
> On Mon, 2 Aug 2010 19:13:04 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
>
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> >
> > Now, memory cgroup has an ID per cgroup and make use of it at
> > - hierarchy walk,
> > - swap recording.
> >
> > This patch is for making more use of it. The final purpose is
> > to replace page_cgroup->mem_cgroup's pointer to an unsigned short.
> >
> > This patch caches a pointer of memcg in an array. By this, we
> > don't have to call css_lookup() which requires radix-hash walk.
> > This saves some amount of memory footprint at lookup memcg via id.
> >
> > Changelog: 20100730
> > - fixed rcu_read_unlock() placement.
> >
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > ---
> > init/Kconfig | 11 +++++++++++
> > mm/memcontrol.c | 48 ++++++++++++++++++++++++++++++++++--------------
> > 2 files changed, 45 insertions(+), 14 deletions(-)
> >
> > Index: mmotm-0727/mm/memcontrol.c
> > ===================================================================
> > --- mmotm-0727.orig/mm/memcontrol.c
> > +++ mmotm-0727/mm/memcontrol.c
> > @@ -292,6 +292,30 @@ static bool move_file(void)
> > &mc.to->move_charge_at_immigrate);
> > }
> >
> > +/* 0 is unused */
> > +static atomic_t mem_cgroup_num;
> > +#define NR_MEMCG_GROUPS (CONFIG_MEM_CGROUP_MAX_GROUPS + 1)
> > +static struct mem_cgroup *mem_cgroups[NR_MEMCG_GROUPS] __read_mostly;
> > +
> > +static struct mem_cgroup *id_to_memcg(unsigned short id)
> > +{
> > + /*
> > + * This array is set to NULL when mem_cgroup is freed.
> > + * IOW, there are no more references && rcu_synchronized().
> > + * This lookup-caching is safe.
> > + */
> > + if (unlikely(!mem_cgroups[id])) {
> > + struct cgroup_subsys_state *css;
> > +
> > + rcu_read_lock();
> > + css = css_lookup(&mem_cgroup_subsys, id);
> > + rcu_read_unlock();
> > + if (!css)
> > + return NULL;
> > + mem_cgroups[id] = container_of(css, struct mem_cgroup, css);
> > + }
> > + return mem_cgroups[id];
> > +}
> id_to_memcg() seems to be called under rcu_read_lock() already, so I think
> rcu_read_lock()/unlock() would be unnecessary.
>
Maybe. I thought about which is better to add
VM_BUG_ON(!rcu_read_lock_held);
or
rcu_read_lock()
..
rcu_read_unlock()
Do you like former ? If so, it's ok to remove rcu-read-lock.
> > Index: mmotm-0727/init/Kconfig
> > ===================================================================
> > --- mmotm-0727.orig/init/Kconfig
> > +++ mmotm-0727/init/Kconfig
> > @@ -594,6 +594,17 @@ config CGROUP_MEM_RES_CTLR_SWAP
> > Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
> > size is 4096bytes, 512k per 1Gbytes of swap.
> >
> > +config MEM_CGROUP_MAX_GROUPS
> > + int "Maximum number of memory cgroups on a system"
> > + range 1 65535
> > + default 8192 if 64BIT
> > + default 2048 if 32BIT
> > + help
> > + Memory cgroup has limitation of the number of groups created.
> > + Please select your favorite value. The more you allow, the more
> > + memory will be consumed. This consumes vmalloc() area, so,
> > + this should be small on 32bit arch.
> > +
> We don't use vmalloc() area in this version :)
>
Oh. yes. thank you. I'll fix
Thanks,
-Kame
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