linux-kernel - Re: Attaching a process to cgroups

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Date:	Wed, 25 Jul 2012 15:57:47 +0200
From:	Mike Galbraith <efault@....de>
To:	Alexey Vlasov <renton@...ton.name>
Cc:	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com
Subject: Re: Attaching a process to cgroups

On Wed, 2012-07-25 at 17:36 +0400, Alexey Vlasov wrote: 
> Hi.
> 
> Now I've got almost 5k used groups and it got even worse. Now I've got
> almost 5k used groups and it got even worse.
> 
> If only write was working slower, now everything connected with cgroups
> is hardly working.
> 
> Could it be connected with synchronize_rcu()?

I'd profile it with perf, and expect to find a large pile of cycles.

> Hanging on read():
> 
> # strace -ttT cat /proc/cgroups 
> 
> 17:30:43.825005 fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 13), ...}) = 0 <0.000005>
> 17:30:43.825048 open("/proc/cgroups", O_RDONLY) = 3 <0.000014>
> 17:30:43.825085 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 <0.000004>
> 17:30:43.825125 fadvise64(3, 0, 0, POSIX_FADV_SEQUENTIAL) = 0 <0.000005>
> 17:30:43.825161 read(3, "#subsys_name\thierarchy\tnum_cgrou"..., 32768) = 112 <7.447084>

Ew.. zillion cgroups is definitely a bad idea.

-Mike

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