linux-kernel - Re: [PATCH] [RFC] pidns: don't zap processes several times

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Date:	Mon, 8 Oct 2012 21:10:28 +0400
From:	Andrey Wagin <avagin@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH] [RFC] pidns: don't zap processes several times

2012/10/7 Oleg Nesterov <oleg@...hat.com>:
> On 10/07, Andrew Vagin wrote:
>>
>> I wrote a test program. It does clone(CLONE_NEWPID | CLONE_VM) and
>> sleep(), a new task repeates the same actions. This program creates
>> 4000 tasks. When I tried to kill all this processes, a system was
>> inaccessible for some minutes.
>
> So this creates 4000 nested namespaces? Not sure this really needs the
> fix... The size of pid would be more than 4000 * sizeof(struct upid).
>
> Perhaps we should MAX_PID_NS_LEVEL instead?

Yes, we can.

Could I just define MAX_PID_NS_LEVEL in a code:
#define MAX_PID_NS_LEVEL ((PAGE_SIZE - offsetof(struct pid, numbers))
/ sizeof(struct upid))

Or should it be added in a config?
My opinion is that MAX_PID_NS_LEVEL can be defined, it will be 126 on
x86_64. I don't know a usecase for which, it will be not enough. When
someone finds a reasonable use case, it can be changed.

>
> As for the patch, it looks correct at first glance. But,

I agree with all your comments.

Thanks.
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