> Sent: Wednesday, March 07, 2018 at 9:28 PM
> From: "Amir Goldstein" <amir73il@xxxxxxxxx>
> To: "Chengguang Xu" <cgxu519@xxxxxxx>
> Cc: overlayfs <linux-unionfs@xxxxxxxxxxxxxxx>, "Miklos Szeredi" <miklos@xxxxxxxxxx>
> Subject: Re: "quota-df" feature
>
> On Wed, Mar 7, 2018 at 2:52 PM, Chengguang Xu <cgxu519@xxxxxxx> wrote:
> > Hello folks,
> >
> > Recently I'm trying to implement a feature on overlayfs for our users.
> > I'd like to call it "quota-df" which means when calling statfs(2),
> > override/update some fields(e.g., total/used/avail of both block/inode counts）
> > using proper project quota information if the quota has already set to
> > underlying directories of overlayfs.
> >
>
> Do you mean project quota setting on underlying fs directories or
> something else?
Underlying fs directories, more accurately the directory include
upperdir && workdir.
>
> > This feature is probably useful for most of container users and there is
> > no serious side effect to the other parts. We can also provide a new
> > mount option to enable/disable the function according to different use cases.
> >
> > Although I'm still working on it but I'll post the RFC patch here for review
> > in recent days and hope to get some feedback from you. Any kind of suggestions
> > are welcomed.
> >
>
> I was asked about quota accounting for the merged content of overalyfs,
> so quota would display a number resembling du -s on the overlay mount.
> This means that "covered" lower files are not accounted for in the merge.
> Is that what you aim to achieve? If not, would that also be an interesting case
> for you to explore?
> Basically, the index directory could be used to reconstruct the entire quota
> information for upper and lower (and copied up) files if full indexing
> is enabled
> with nfs_export=on.
To be honest, our use case is standard docker container with overlayfs and
our requirement of quota-df is accurately counting usage/avail inside container.
Lowerdirs could be share with different overlayfs, so I'm not sure counting
the contents of lowerdirs is proper behavior or not. If lowerdirs are dedicated
to one overlayfs then maybe setting same project id with upperdir can resolve
"covered" problem that you mentioned above. Counting usage information without
quota might be a hard work when having plenty of files.
I don't know exactly what will happen when combining index and nfs_export options,
I need to read and understand related code later.
>
> >
> > Here are some test examples share with you (based on ext4):
> >
> > 1) project quota enabled && without hard-limit
> >
> > $ df -h /mnt/test3 /mnt/test3/df/merged
> > Filesystem Size Used Avail Use% Mounted on
> > /dev/vdb3 99G 2.5G 91G 3% /mnt/test3
> > overlay 92G 201M 91G 1% /mnt/test3/df/merged
> >
> > $ df -hi /mnt/test3 /mnt/test3/df/merged
> > Filesystem Inodes IUsed IFree IUse% Mounted on
> > /dev/vdb3 6.3M 2.4K 6.3M 1% /mnt/test3
> > overlay 6.3M 8 6.3M 1% /mnt/test3/df/merged
> >
> > 2) project quota enabled && with hard-limit
> >
> > $ df -h /mnt/test3 /mnt/test3/df/merged
> > Filesystem Size Used Avail Use% Mounted on
> > /dev/vdb3 99G 2.5G 91G 3% /mnt/test3
> > overlay 1.0G 201M 824M 20% /mnt/test3/df/merged
> >
> > $ df -hi /mnt/test3 /mnt/test3/df/merged
> > Filesystem Inodes IUsed IFree IUse% Mounted on
> > /dev/vdb3 6.3M 2.4K 6.3M 1% /mnt/test3
> > overlay 1000 8 992 1% /mnt/test3/df/merged
> >
> >
>
> I can't follow from the example below what is the expected result and why
> if you add the quota setup commands that could be useful.
Underlying fs using ext4 and mkfs/mount with project quota option and
all needed directories(lowerdir, upperdir, workdir, merged) are set same
project quota. Current quota-df implementation only adjust the couting
information when having upperdir.
In case 1:
There is no hardlimit/softlimit, so the expected result as below.
Used: The used count in project quota which set to the directory
include upperdir && workdir.
Avail: The avail of underlying fs
Total: Used + Avail
#upperdir used 201M and /mnt/test3 used 2.5G
In case 2:
Project quota hardlimits are block count = 1G, inode count = 1000.
So the expected result as below.
Used: The used count in project quota which set to the directory
include upperdir && workdir.
Avail: (a)Hardlimit - Used or (b)The avail of underlying fs(when a > b)
Total: Used + Avail
Thanks,
Chengguang.
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