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

From: Topi Miettinen <toiwoton@gmail.com>
To: Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org, Li Zefan <lizefan@huawei.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	"open list:CONTROL GROUP (CGROUP)" <cgroups@vger.kernel.org>
Subject: Re: [RFC 02/18] cgroup_pids: track maximum pids
Date: Mon, 13 Jun 2016 21:59:32 +0000	[thread overview]
Message-ID: <15ef1041-35b6-cb31-ff98-8b0be7780bc3@gmail.com> (raw)
In-Reply-To: <20160613213354.GH31708@htj.duckdns.org>

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