Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 3 Mar 2021 22:12:32 -0800
From:   Vipin Sharma <vipinsh@google.com>
To:     Tejun Heo <tj@kernel.org>
Cc:     mkoutny@suse.com, rdunlap@infradead.org, thomas.lendacky@amd.com,
        brijesh.singh@amd.com, jon.grimm@amd.com, eric.vantassell@amd.com,
        pbonzini@redhat.com, hannes@cmpxchg.org, frankja@linux.ibm.com,
        borntraeger@de.ibm.com, corbet@lwn.net, seanjc@google.com,
        vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com,
        joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com,
        bp@alien8.de, hpa@zytor.com, gingell@google.com,
        rientjes@google.com, dionnaglaze@google.com, kvm@vger.kernel.org,
        x86@kernel.org, cgroups@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC v2 1/2] cgroup: sev: Add misc cgroup controller
Message-ID: <YEB6ULUgbf+s8ydd@google.com>
References: <20210302081705.1990283-1-vipinsh@google.com>
 <20210302081705.1990283-2-vipinsh@google.com>
 <YD+ubbB4Tz0ZlVvp@slm.duckdns.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <YD+ubbB4Tz0ZlVvp@slm.duckdns.org>
Precedence: bulk

On Wed, Mar 03, 2021 at 10:42:37AM -0500, Tejun Heo wrote:
> > +	atomic_t usage;
> > +};
> 
> Can we do 64bits so that something which counts memory can use this too?
> 
Sure.

> > +
> > +		if (usage > capacity)
> > +			return -EBUSY;
> 
> I'd rather go with allowing bringing down capacity below usage so that the
> users can set it to a lower value to drain existing usages while denying new
> ones. It's not like it's difficult to check the current total usage from the
> caller side, so I'm not sure it's very useful to shift the condition check
> here.
> 

Okay, I will change the code to set new capacity unconditionally.

Right now there is no API for the caller to know total usage, unless they
keep their own tally, I was thinking it will be useful to add one more API

unsigned long misc_cg_res_total_usage(enum misc_res_type type)

It will return root_cg usage for "type" resource.
Will it be fine?

> > +			pr_info("cgroup: charge rejected by misc controller for %s resource in ",
> > +				misc_res_name[type]);
> > +			pr_cont_cgroup_path(i->css.cgroup);
> > +			pr_cont("\n");
> 
> Should have commented on this in the priv thread but don't print something
> on every rejection. This often becomes a nuisance and can make an easy DoS
> vector at worst. If you wanna do it, print it once per cgroup or sth like
> that.

I didn't think in that way. Thanks, I will print it once per cgroup.

Thanks
Vipin