Re: [PATCH 2/4] memcg: prevent changes to move_charge_at_immigrate during task attach
From: Michal Hocko <hidden>
Date: 2012-12-04 09:29:46
Also in:
linux-mm
On Fri 30-11-12 17:31:24, Glauber Costa wrote:
Currently, we rely on the cgroup_lock() to prevent changes to move_charge_at_immigrate during task migration. We can do something similar to what cpuset is doing, and flip a flag to tell us if task movement is taking place. In theory, we could busy loop waiting for that value to return to 0 - it will eventually. But I am judging that returning EAGAIN is not too much of a problem, since file writers already should be checking for error codes anyway.
I think we should prevent from EAGAIN because this is a behavior change. Why not just loop with signal_pending test for breaking out and a small sleep after attach_in_progress > 0 && unlock?
quoted hunk ↗ jump to hunk
Signed-off-by: Glauber Costa <redacted> --- mm/memcontrol.c | 64 +++++++++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 51 insertions(+), 13 deletions(-)diff --git a/mm/memcontrol.c b/mm/memcontrol.c index feba87d..d80b6b5 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c@@ -311,7 +311,13 @@ struct mem_cgroup { * Should we move charges of a task when a task is moved into this * mem_cgroup ? And what type of charges should we move ? */ - unsigned long move_charge_at_immigrate; + unsigned long move_charge_at_immigrate; + /* + * Tasks are being attached to this memcg. Used mostly to prevent + * changes to move_charge_at_immigrate + */ + int attach_in_progress; + /* * set > 0 if pages under this cgroup are moving to other cgroup. */@@ -4114,6 +4120,7 @@ static int mem_cgroup_move_charge_write(struct cgroup *cgrp, struct cftype *cft, u64 val) { struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp); + int ret = -EAGAIN; if (val >= (1 << NR_MOVE_TYPE)) return -EINVAL;@@ -4123,10 +4130,13 @@ static int mem_cgroup_move_charge_write(struct cgroup *cgrp, * inconsistent. */ cgroup_lock(); + if (memcg->attach_in_progress) + goto out; memcg->move_charge_at_immigrate = val; + ret = 0; +out: cgroup_unlock(); - - return 0; + return ret; } #else static int mem_cgroup_move_charge_write(struct cgroup *cgrp,@@ -5443,12 +5453,12 @@ static void mem_cgroup_clear_mc(void) mem_cgroup_end_move(from); } -static int mem_cgroup_can_attach(struct cgroup *cgroup, - struct cgroup_taskset *tset) + +static int __mem_cgroup_can_attach(struct mem_cgroup *memcg, + struct cgroup_taskset *tset) { struct task_struct *p = cgroup_taskset_first(tset); int ret = 0; - struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup); if (memcg->move_charge_at_immigrate) { struct mm_struct *mm;@@ -5482,8 +5492,8 @@ static int mem_cgroup_can_attach(struct cgroup *cgroup, return ret; } -static void mem_cgroup_cancel_attach(struct cgroup *cgroup, - struct cgroup_taskset *tset) +static void __mem_cgroup_cancel_attach(struct mem_cgroup *memcg, + struct cgroup_taskset *tset) { mem_cgroup_clear_mc(); }@@ -5630,8 +5640,8 @@ retry: up_read(&mm->mmap_sem); } -static void mem_cgroup_move_task(struct cgroup *cont, - struct cgroup_taskset *tset) +static void __mem_cgroup_move_task(struct mem_cgroup *memcg, + struct cgroup_taskset *tset) { struct task_struct *p = cgroup_taskset_first(tset); struct mm_struct *mm = get_task_mm(p);@@ -5645,20 +5655,48 @@ static void mem_cgroup_move_task(struct cgroup *cont, mem_cgroup_clear_mc(); } #else /* !CONFIG_MMU */ +static int __mem_cgroup_can_attach(struct mem_cgroup *memcg, + struct cgroup_taskset *tset) +{ + return 0; +} + +static void __mem_cgroup_cancel_attach(struct mem_cgroup *memcg, + struct cgroup_taskset *tset) +{ +} + +static void __mem_cgroup_move_task(struct mem_cgroup *memcg, + struct cgroup_taskset *tset) +{ +} +#endif static int mem_cgroup_can_attach(struct cgroup *cgroup, struct cgroup_taskset *tset) { - return 0; + struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup); + + memcg->attach_in_progress++; + return __mem_cgroup_can_attach(memcg, tset); } + static void mem_cgroup_cancel_attach(struct cgroup *cgroup, struct cgroup_taskset *tset) { + struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup); + + __mem_cgroup_cancel_attach(memcg, tset); + memcg->attach_in_progress--; } -static void mem_cgroup_move_task(struct cgroup *cont, + +static void mem_cgroup_move_task(struct cgroup *cgroup, struct cgroup_taskset *tset) { + struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup); + + __mem_cgroup_move_task(memcg, tset); + memcg->attach_in_progress--; } -#endif struct cgroup_subsys mem_cgroup_subsys = { .name = "memory",-- 1.7.11.7
-- Michal Hocko SUSE Labs