Re: [PATCH v16 08/11] secretmem: add memcg accounting

[Mike Rapoport <rppt@kernel.org>]

On Mon, Jan 25, 2021 at 09:18:04AM -0800, Shakeel Butt wrote:
> On Mon, Jan 25, 2021 at 8:20 AM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Thu, Jan 21, 2021 at 02:27:20PM +0200, Mike Rapoport wrote:
> > > From: Mike Rapoport <rppt@linux.ibm.com>
> > >
> > > Account memory consumed by secretmem to memcg. The accounting is updated
> > > when the memory is actually allocated and freed.

I though about doing per-page accounting, but then one would be able to
create a lot of secretmem file descriptors, use only a page from each while
actual memory consumption will be way higher.

> > I think this is wrong.  It fails to account subsequent allocators from
> > the same PMD.  If you want to track like this, you need separate pools
> > per memcg.
> >
> 
> Are these secretmem pools shared between different jobs/memcgs?

A secretmem pool is per anonymous file descriptor and this file descriptor
can be shared only explicitly between several processes. So, the secretmem
pool should not be shared between different jobs/memcg. Of course, it's
possible to spread threads of a process across different memcgs, but in
that case the accounting will be similar to what's happening today with
sl*b. The first thread to cause kmalloc() will be charged for the
allocation of the entire slab and subsequent allocations from that slab
will not be accounted.

That said, having a pool per memcg will add ton of complexity with very
dubious value.

-- 
Sincerely yours,
Mike.
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