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SubjectRe: [RFC][PATCH 4/4] memcg: make oom less frequently
On Thu, 8 Jan 2009 20:19:48 +0900 (JST), "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> Daisuke Nishimura said:
> > In previous implementation, mem_cgroup_try_charge checked the return
> > value of mem_cgroup_try_to_free_pages, and just retried if some pages
> > had been reclaimed.
> > But now, try_charge(and mem_cgroup_hierarchical_reclaim called from it)
> > only checks whether the usage is less than the limit.
> >
> > This patch tries to change the behavior as before to cause oom less
> > frequently.
> >
> > To prevent try_charge from getting stuck in infinite loop,
> > MEM_CGROUP_RECLAIM_RETRIES_MAX is defined.
> >
> >
> > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
>
> I think this is necessary change.
> My version of hierarchy reclaim will do this.
>
> But RETRIES_MAX is not clear ;) please use one counter.
>
> And why MAX=32 ?
I inserted printk and counted the loop count on oom(tested with 4 children).
It seemed 32 would be enough.

> > + if (ret)
> > + continue;
> seems to do enough work.
>
> While memory can be reclaimed, it's not dead lock.
I see.
I introduced this max count because mmap_sem might be hold for a long time
at page fault, but this is not "dead" lock as you say.

> To handle live-lock situation as "reclaimed memory is stolen very soon",
> should we check signal_pending(current) or some flags ?
>
> IMHO, using jiffies to detect how long we should retry is easy to understand
> ....like
> "if memory charging cannot make progress for XXXX minutes,
> trigger some notifier or show some flag to user via cgroupfs interface.
> to show we're tooooooo busy."
>
Good Idea.

But I think it would be enough for now to check signal_pending(curren) and
return -ENOMEM.

How about this one?
===
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

In previous implementation, mem_cgroup_try_charge checked the return
value of mem_cgroup_try_to_free_pages, and just retried if some pages
had been reclaimed.
But now, try_charge(and mem_cgroup_hierarchical_reclaim called from it)
only checks whether the usage is less than the limit.

This patch tries to change the behavior as before to cause oom less frequently.


Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
mm/memcontrol.c | 14 ++++++++++----
1 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index dc38a0e..2ab0a5c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -770,10 +770,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
* but there might be left over accounting, even after children
* have left.
*/
- ret = try_to_free_mem_cgroup_pages(root_mem, gfp_mask, noswap,
+ ret += try_to_free_mem_cgroup_pages(root_mem, gfp_mask, noswap,
get_swappiness(root_mem));
if (mem_cgroup_check_under_limit(root_mem))
- return 0;
+ return 1; /* indicate reclaim has succeeded */
if (!root_mem->use_hierarchy)
return ret;

@@ -784,10 +784,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
next_mem = mem_cgroup_get_next_node(root_mem);
continue;
}
- ret = try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap,
+ ret += try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap,
get_swappiness(next_mem));
if (mem_cgroup_check_under_limit(root_mem))
- return 0;
+ return 1; /* indicate reclaim has succeeded */
next_mem = mem_cgroup_get_next_node(root_mem);
}
return ret;
@@ -870,8 +870,13 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
if (!(gfp_mask & __GFP_WAIT))
goto nomem;

+ if (signal_pending(current))
+ goto oom;
+
ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, gfp_mask,
noswap);
+ if (ret)
+ continue;

/*
* try_to_free_mem_cgroup_pages() might not give us a full
@@ -885,6 +890,7 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
continue;

if (!nr_retries--) {
+oom:
if (oom) {
mutex_lock(&memcg_tasklist);
mem_cgroup_out_of_memory(mem_over_limit, gfp_mask);

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