linux-kernel - Re: [PATCH v14 02/14] cgroup/misc: Add per resource callbacks for CSS events

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Date: Fri, 07 Jun 2024 09:23:16 -0500
From: "Haitao Huang" <haitao.huang@...ux.intel.com>
To: jarkko@...nel.org, dave.hansen@...ux.intel.com, kai.huang@...el.com,
 tj@...nel.org, mkoutny@...e.com, linux-kernel@...r.kernel.org,
 linux-sgx@...r.kernel.org, x86@...nel.org, cgroups@...r.kernel.org,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
 sohil.mehta@...el.com, tim.c.chen@...ux.intel.com, chenridong
 <chenridong@...wei.com>
Cc: zhiquan1.li@...el.com, kristen@...ux.intel.com, seanjc@...gle.com,
 zhanb@...rosoft.com, anakrish@...rosoft.com, mikko.ylinen@...ux.intel.com,
 yangjie@...rosoft.com, chrisyan@...rosoft.com
Subject: Re: [PATCH v14 02/14] cgroup/misc: Add per resource callbacks for CSS
 events

On Thu, 06 Jun 2024 20:53:11 -0500, chenridong <chenridong@...wei.com>  
wrote:

> I think it is better when _misc_cg_res_alloc fails, it just calls  
> _misc_cg_res_free(cg, index)(add index parameter, it means ending of  
> iterator), so it can avoid calling ->free() that do not call ->alloc().
>
> And in misc_cg_free, just call _misc_cg_res_free(cg, MISC_CG_RES_TYPES)   
> to free all.
>
That makes sense now, Will do that.
(BTW you need comment inline :-)
Thanks
Haitao

>
> On 2024/6/6 22:51, Haitao Huang wrote:
>> On Thu, 06 Jun 2024 08:37:31 -0500, chenridong <chenridong@...wei.com>  
>> wrote:
>>
>>>
>>>   If _misc_cg_res_alloc fails, maybe some types do not call ->alloc(),  
>>> but all types ->free() callback >will be called, is that ok?
>>>
>> Not sure I understand. Are you suggesting we ignore failures from  
>> ->alloc() callback in _misc_cg_res_alloc() as it is per-resource, and  
>> have ->free() callback and resource provider of the failing type to  
>> handle the failure internally?
>>
>> IIUC, this failure only happens when a specific subcgroup is created  
>> (memory running out for allocation) so failing that subcgroup as a  
>> whole seems fine to me. Note the root node is static and no  
>> pre-resource callbacks invoked by misc. And resource provider handles  
>> its own allocations for root. In SGX case we too declare a static  
>> object for corresponding root sgx_cgroup struct.
>>
>> Note also misc cgroup (except for setting capacity[res] = 0 at root) is  
>> all or nothing so no mechanism to tell user "this resource does not  
>> work but others are fine in this particular cgroup."
>>
>> Thanks
>> Haitao
>>
>


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