linux-ext4 - Re: container disk quota

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Date:	Sun, 03 Jun 2012 12:23:39 +0800
From:	Jeff Liu <jeff.liu@...cle.com>
To:	Kirill Korotaev <dev@...allels.com>
CC:	Serge Hallyn <serge.hallyn@...onical.com>,
	"tytso@....edu" <tytso@....edu>,
	"tinguely@....com" <tinguely@....com>,
	"containers@...ts.linux-foundation.org" 
	<containers@...ts.linux-foundation.org>,
	"david@...morbit.com" <david@...morbit.com>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	"hch@...radead.org" <hch@...radead.org>,
	"bpm@....com" <bpm@....com>,
	"christopher.jones@...cle.com" <christopher.jones@...cle.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Jan Kara <jack@...e.cz>, "tm@....ma" <tm@....ma>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"chris.mason@...cle.com" <chris.mason@...cle.com>
Subject: Re: container disk quota

Hi Kirill,

On 06/02/2012 11:21 PM, Kirill Korotaev wrote:

>>>>>
>>>>> Not having looked closely at the original patchset, let me ask - is this
>>>>> feature going to be a freebie with Eric's usernamespace patches?
>>>>
>>>> It we can reach a consensus to bind quota on mount namespace for
>>>> container or other things maybe.
>>>
>>> 1. OpenVZ doesn't use mount namespaces and still has quotas per container.
>>
>> AFAICS, OpenVZ has self-released quota tools to supply this feature.
> 
> but standard quota tools work inside container w/o any modifications.
> This is very important for us, cause we run unmodified distros inside.

Yes, am agree.
I can work out a new patches regarding quota tools based on mount namespace w/o any modification.

> 
> Actually, this is unrelated. I meant that OpenVZ needs ability to have group quotas w/o mount namespaces.
> 
>>
>>>
>>> 2. BTW, have you seen Dmitry Monakhov patches for same containers quotas via additional inode attribute? it allows to make it journaled.
>>
>> You means the directly/project quota on ext4?
>> If yes, I have observed this feature back to the end of last year in
>> EXT4 mail list.
> 
> yes
> 
>>
>>> How quotas are stored in your case?
>>
>> It simply cached at memory for now, it also can be tweak up to journaled
>> I think, if introducing corresponding routines quota_read/quota_write to
>> particular journal file system.
> 
> just cached quotas are bad - you never sure they are correct.
> journaled quotas (as standart) are much better.

Exactly.

> 
>>
>>>
>>> 3. I tend to think nowdays such quotas maybe of less need. Quota code doesn't scale well. And it's easier to put container in image file (as OpenVZ recently introduced).
>>
>> There have such requirements dropped to LXC mail list nowadays.
>> Directory quota is pretty cool and it also useful to containers perspective.
>>
>> However, that's two different quota mechanism.
>>
>> "Quota code doesn't scale well".
>> Do you means it have global locking mechanism and only quota structure
>> to bill up quota for all file systems with VFS quota enabled?
> 
> yes.

That's also means there has a potential opportunity for improvement in terms of scalability.

Thanks for your info!
-Jeff

> 
> Kirill
> 


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