linux-ext4 - Re: container disk quota

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Date:	Sat, 2 Jun 2012 19:21:17 +0400
From:	Kirill Korotaev <dev@...allels.com>
To:	"jeff.liu@...cle.com" <jeff.liu@...cle.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

>>>> 
>>>> 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.

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.

> 
>> 
>> 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.

Kirill

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