From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: linux-mm@kvack.org, "balbir@linux.vnet.ibm.com" <balbir@linux.vnet.ibm.com>, gthelen@google.com, m-ikeda@ds.jp.nec.com, "akpm@linux-foundation.org" <akpm@linux-foundation.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "menage@google.com" <menage@google.com>, "lizf@cn.fujitsu.com" <lizf@cn.fujitsu.com>, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Subject: Re: [PATCH 4/5] memcg: lockless update of file stat with move-account safe method Date: Tue, 31 Aug 2010 12:51:18 +0900 [thread overview] Message-ID: <20100831125118.fa01f0c2.nishimura@mxp.nes.nec.co.jp> (raw) In-Reply-To: <20100825171050.1574ba7c.kamezawa.hiroyu@jp.fujitsu.com> On Wed, 25 Aug 2010 17:10:50 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > At accounting file events per memory cgroup, we need to find memory cgroup > via page_cgroup->mem_cgroup. Now, we use lock_page_cgroup(). > > But, considering the context which page-cgroup for files are accessed, > we can use alternative light-weight mutual execusion in the most case. > At handling file-caches, the only race we have to take care of is "moving" > account, IOW, overwriting page_cgroup->mem_cgroup. Because file status > update is done while the page-cache is in stable state, we don't have to > take care of race with charge/uncharge. > > Unlike charge/uncharge, "move" happens not so frequently. It happens only when > rmdir() and task-moving (with a special settings.) > This patch adds a race-checker for file-cache-status accounting v.s. account > moving. The new per-cpu-per-memcg counter MEM_CGROUP_ON_MOVE is added. > The routine for account move > 1. Increment it before start moving > 2. Call synchronize_rcu() > 3. Decrement it after the end of moving. > By this, file-status-counting routine can check it needs to call > lock_page_cgroup(). In most case, I doesn't need to call it. > > Changelog: 20100825 > - added a comment about mc.lock > - fixed bad lock. > Changelog: 20100804 > - added a comment for possible optimization hint. > Changelog: 20100730 > - some cleanup. > Changelog: 20100729 > - replaced __this_cpu_xxx() with this_cpu_xxx > (because we don't call spinlock) > - added VM_BUG_ON(). > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> (snip) > @@ -1505,29 +1551,36 @@ void mem_cgroup_update_file_mapped(struc > { > struct mem_cgroup *mem; > struct page_cgroup *pc; > + bool need_lock = false; > > pc = lookup_page_cgroup(page); > if (unlikely(!pc)) > return; > - > - lock_page_cgroup(pc); > + rcu_read_lock(); > mem = id_to_memcg(pc->mem_cgroup, true); It doesn't cause any problem, but I think it would be better to change this to "id_to_memcg(..., false)". It's just under rcu_read_lock(), not under page_cgroup lock anymore. Otherwise, it looks good to me. Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Thanks, Daisuke Nishimura.
WARNING: multiple messages have this Message-ID (diff)
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: linux-mm@kvack.org, "balbir@linux.vnet.ibm.com" <balbir@linux.vnet.ibm.com>, gthelen@google.com, m-ikeda@ds.jp.nec.com, "akpm@linux-foundation.org" <akpm@linux-foundation.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "menage@google.com" <menage@google.com>, "lizf@cn.fujitsu.com" <lizf@cn.fujitsu.com>, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Subject: Re: [PATCH 4/5] memcg: lockless update of file stat with move-account safe method Date: Tue, 31 Aug 2010 12:51:18 +0900 [thread overview] Message-ID: <20100831125118.fa01f0c2.nishimura@mxp.nes.nec.co.jp> (raw) In-Reply-To: <20100825171050.1574ba7c.kamezawa.hiroyu@jp.fujitsu.com> On Wed, 25 Aug 2010 17:10:50 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > At accounting file events per memory cgroup, we need to find memory cgroup > via page_cgroup->mem_cgroup. Now, we use lock_page_cgroup(). > > But, considering the context which page-cgroup for files are accessed, > we can use alternative light-weight mutual execusion in the most case. > At handling file-caches, the only race we have to take care of is "moving" > account, IOW, overwriting page_cgroup->mem_cgroup. Because file status > update is done while the page-cache is in stable state, we don't have to > take care of race with charge/uncharge. > > Unlike charge/uncharge, "move" happens not so frequently. It happens only when > rmdir() and task-moving (with a special settings.) > This patch adds a race-checker for file-cache-status accounting v.s. account > moving. The new per-cpu-per-memcg counter MEM_CGROUP_ON_MOVE is added. > The routine for account move > 1. Increment it before start moving > 2. Call synchronize_rcu() > 3. Decrement it after the end of moving. > By this, file-status-counting routine can check it needs to call > lock_page_cgroup(). In most case, I doesn't need to call it. > > Changelog: 20100825 > - added a comment about mc.lock > - fixed bad lock. > Changelog: 20100804 > - added a comment for possible optimization hint. > Changelog: 20100730 > - some cleanup. > Changelog: 20100729 > - replaced __this_cpu_xxx() with this_cpu_xxx > (because we don't call spinlock) > - added VM_BUG_ON(). > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> (snip) > @@ -1505,29 +1551,36 @@ void mem_cgroup_update_file_mapped(struc > { > struct mem_cgroup *mem; > struct page_cgroup *pc; > + bool need_lock = false; > > pc = lookup_page_cgroup(page); > if (unlikely(!pc)) > return; > - > - lock_page_cgroup(pc); > + rcu_read_lock(); > mem = id_to_memcg(pc->mem_cgroup, true); It doesn't cause any problem, but I think it would be better to change this to "id_to_memcg(..., false)". It's just under rcu_read_lock(), not under page_cgroup lock anymore. Otherwise, it looks good to me. Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Thanks, Daisuke Nishimura. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2010-08-31 3:54 UTC|newest] Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-08-25 8:04 [PATCH 0/5] memcg: towards I/O aware memcg v6 KAMEZAWA Hiroyuki 2010-08-25 8:04 ` KAMEZAWA Hiroyuki 2010-08-25 8:06 ` [PATCH 1/5] cgroup: do ID allocation under css allocator KAMEZAWA Hiroyuki 2010-08-25 8:06 ` KAMEZAWA Hiroyuki 2010-08-25 14:15 ` Balbir Singh 2010-08-25 14:15 ` Balbir Singh 2010-08-26 0:13 ` KAMEZAWA Hiroyuki 2010-08-26 0:13 ` KAMEZAWA Hiroyuki 2010-08-31 6:33 ` Balbir Singh 2010-08-31 6:33 ` Balbir Singh 2010-08-30 5:44 ` Daisuke Nishimura 2010-08-30 5:44 ` Daisuke Nishimura 2010-08-25 8:07 ` [PATCH 2/5] memcg: quick memcg lookup array KAMEZAWA Hiroyuki 2010-08-25 8:07 ` KAMEZAWA Hiroyuki 2010-08-30 8:03 ` Daisuke Nishimura 2010-08-30 8:03 ` Daisuke Nishimura 2010-09-01 0:29 ` KAMEZAWA Hiroyuki 2010-09-01 0:29 ` KAMEZAWA Hiroyuki 2010-08-31 7:14 ` Balbir Singh 2010-08-31 7:14 ` Balbir Singh 2010-09-01 0:21 ` KAMEZAWA Hiroyuki 2010-09-01 0:21 ` KAMEZAWA Hiroyuki 2010-08-25 8:09 ` [PATCH 3/5] memcg: use ID instead of pointer in page_cgroup KAMEZAWA Hiroyuki 2010-08-25 8:09 ` KAMEZAWA Hiroyuki 2010-08-31 2:14 ` Daisuke Nishimura 2010-08-31 2:14 ` Daisuke Nishimura 2010-08-25 8:10 ` [PATCH 4/5] memcg: lockless update of file stat with move-account safe method KAMEZAWA Hiroyuki 2010-08-25 8:10 ` KAMEZAWA Hiroyuki 2010-08-31 3:51 ` Daisuke Nishimura [this message] 2010-08-31 3:51 ` Daisuke Nishimura 2010-09-01 0:31 ` KAMEZAWA Hiroyuki 2010-09-01 0:31 ` KAMEZAWA Hiroyuki 2010-08-25 8:11 ` [PATCH 5/5] memcg: generic file stat accounting interface KAMEZAWA Hiroyuki 2010-08-25 8:11 ` KAMEZAWA Hiroyuki 2010-08-31 4:33 ` Daisuke Nishimura 2010-08-31 4:33 ` Daisuke Nishimura 2010-09-01 0:31 ` KAMEZAWA Hiroyuki 2010-09-01 0:31 ` KAMEZAWA Hiroyuki
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