Re: [PATCH v2 1/3] quota: add quota in-memory format support

[Lukas Czerner <lczerner@redhat.com>]

On Tue, Nov 22, 2022 at 11:58:33PM -0800, Christoph Hellwig wrote:
> On Tue, Nov 22, 2022 at 03:21:17PM +0100, Lukas Czerner wrote:
> > > That seems like a good idea for memory usage, but I think this might
> > > also make the code much simpler, as that just requires fairly trivial
> > > quota_read and quota_write methods in the shmem code instead of new
> > > support for an in-memory quota file.
> > 
> > You mean like the implementation in the v1 ?
> 
> Having now found it: yes.
> 

Jan,

do you have any argument for this, since it was your suggestion?

I also think that the implementation is much simpler with in-memory
dquots because we will avoid all the hassle with creating and
maintaining quota file in a proper format. It's not just reads and
writes it's the entire machinery befind it in quota_v2.c and quota_tree.c.

But it is true that even with only user modified dquots being
non-reclaimable until unmount it could theoreticaly represent a
substantial memory consumption. Although I do wonder if this problem
is even real. How many user/group ids would you expect extremely heavy
quota user would have the limits set for? 1k, 10k, million, or even
more? Do you know?

-Lukas