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Date: Tue, 3 Aug 2010 13:37:23 +0900 From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> To: Daisuke Nishimura <nishimura@....nes.nec.co.jp> Cc: linux-mm@...ck.org, "balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>, vgoyal@...hat.com, m-ikeda@...jp.nec.com, gthelen@...gle.com, "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH -mm 1/5] quick lookup memcg by ID On Tue, 3 Aug 2010 13:31:09 +0900 Daisuke Nishimura <nishimura@....nes.nec.co.jp> 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@...fujitsu.com> wrote: > > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> > > > > 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@...fujitsu.com> > > --- > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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