Messages in this thread | | | Date | Tue, 9 Dec 2008 09:18:28 +0530 | From | Balbir Singh <> | Subject | Re: [mm] [PATCH 3/4] Memory cgroup hierarchical reclaim (v4) |
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* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2008-12-09 11:59:43]:
> On Wed, 26 Nov 2008 11:14:47 +0900 > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote: > > > On Tue, 25 Nov 2008 20:31:25 +0530, Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > > Daisuke Nishimura wrote: > > > > Hi. > > > > > > > > Unfortunately, trying to hold cgroup_mutex at reclaim causes dead lock. > > > > > > > > For example, when attaching a task to some cpuset directory(memory_migrate=on), > > > > > > > > cgroup_tasks_write (hold cgroup_mutex) > > > > attach_task_by_pid > > > > cgroup_attach_task > > > > cpuset_attach > > > > cpuset_migrate_mm > > > > : > > > > unmap_and_move > > > > mem_cgroup_prepare_migration > > > > mem_cgroup_try_charge > > > > mem_cgroup_hierarchical_reclaim > > > > > > > > > > Did lockdep complain about it? > > > > > I haven't understood lockdep so well, but I got logs like this: > > > > === > > INFO: task move.sh:17710 blocked for more than 480 seconds. > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > > move.sh D ffff88010e1c76c0 0 17710 17597 > > ffff8800bd9edf00 0000000000000046 0000000000000000 0000000000000000 > > ffff8803afbc0000 ffff8800bd9ee270 0000000e00000000 000000010a54459c > > ffffffffffffffff ffffffffffffffff ffffffffffffffff 7fffffffffffffff > > Call Trace: > > [<ffffffff802ae9f0>] mem_cgroup_get_first_node+0x29/0x8a > > [<ffffffff804cb357>] mutex_lock_nested+0x180/0x2a2 > > [<ffffffff802ae9f0>] mem_cgroup_get_first_node+0x29/0x8a > > [<ffffffff802ae9f0>] mem_cgroup_get_first_node+0x29/0x8a > > [<ffffffff802aed9c>] __mem_cgroup_try_charge+0x27a/0x2de > > [<ffffffff802afdfd>] mem_cgroup_prepare_migration+0x6c/0xa5 > > [<ffffffff802ad97f>] migrate_pages+0x10c/0x4a0 > > [<ffffffff802ad9c8>] migrate_pages+0x155/0x4a0 > > [<ffffffff802a14cb>] new_node_page+0x0/0x2f > > [<ffffffff802a1adb>] check_range+0x300/0x325 > > [<ffffffff802a2374>] do_migrate_pages+0x1a5/0x1f1 > > [<ffffffff8026d272>] cpuset_migrate_mm+0x30/0x93 > > [<ffffffff8026d29c>] cpuset_migrate_mm+0x5a/0x93 > > [<ffffffff8026df41>] cpuset_attach+0x93/0xa6 > > [<ffffffff8026ae1b>] cgroup_attach_task+0x395/0x3e1 > > [<ffffffff8026af61>] cgroup_tasks_write+0xfa/0x11d > > [<ffffffff8026aea0>] cgroup_tasks_write+0x39/0x11d > > [<ffffffff8026b5aa>] cgroup_file_write+0xef/0x216 > > [<ffffffff802b2968>] vfs_write+0xad/0x136 > > [<ffffffff802b2dfe>] sys_write+0x45/0x6e > > [<ffffffff8020bdab>] system_call_fastpath+0x16/0x1b > > INFO: lockdep is turned off. > > === > > > > And other processes trying to hold cgroup_mutex are also stuck. > > > > > 1. We could probably move away from cgroup_mutex to a memory controller specific > > > mutex. > > > 2. We could give up cgroup_mutex before migrate_mm, since it seems like we'll > > > hold the cgroup lock for long and holding it during reclaim will definitely be > > > visible to users trying to create/delete nodes. > > > > > > I prefer to do (2), I'll look at the code more closely > > > > > I basically agree, but I think we should also consider mpol_rebind_mm. > > > > mpol_rebind_mm, which can be called from cpuset_attach, does down_write(mm->mmap_sem), > > which means down_write(mm->mmap_sem) can be called under cgroup_mutex. > > OTOH, page fault path does down_read(mm->mmap_sem) and can call mem_cgroup_try_charge, > > which means mutex_lock(cgroup_mutex) can be called under down_read(mm->mmap_sem). > > > > What's status of this problem ? fixed or not yet ? > Sorry for failing to track paches. >
Kamezawa-San,
We are looking at two approaches that I had mentioned earlier
1) rely on the new cgroup_tasklist mutex introduced to close the race 2) Removing cgroup lock dependency with cgroup_tasks_write. I worry that it can lead to long latencies with cgroup_lock held
I can send a patch for (1) today, I want to fix (2) and spent a lot of time staring at that code and could not find any easy way to fix it.
-- Balbir
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