linux-kernel - Re: [RFC 02/18] cgroup_pids: track maximum pids

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Date:	Mon, 13 Jun 2016 21:59:32 +0000
From:	Topi Miettinen <toiwoton@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>
Subject: Re: [RFC 02/18] cgroup_pids: track maximum pids

On 06/13/16 21:33, Tejun Heo wrote:
> Hello,
> 
> On Mon, Jun 13, 2016 at 09:29:32PM +0000, Topi Miettinen wrote:
>> I used fork callback as I don't want to lower the watermark in all cases
>> where the charge can be lowered, so I'd update the watermark only when
>> the fork really happens.
> 
> I don't think that would make a noticeable difference.  That's where
> we decide whether to grant fork or not after all and thus where the
> actual usage is.
> 

You mean, increment count on cgroup_can_fork()? But what if the fork()
fails after that (signal_pending case)?

>> Is there a better way to compare and set? I don't think atomic_cmpxchg()
>> does what's needed,
> 
> cmpxchg loop should do what's necessary although I'm not sure how much
> being strictly correct matters here.
> 
> Thanks.
> 

These are not used for any decisions taken by kernel, but by the user. I
have to say I don't know where's the line between strict correctness and
less strict.

-Topi