Re: [PATCH v2 0/3] Directed kmem charging

[Andrew Morton]

On Wed, 21 Feb 2018 09:18:35 -0800 Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:

> On Wed, Feb 21, 2018 at 8:09 AM, Christopher Lameter <cl@xxxxxxxxx> wrote:
> > Another way to solve this is to switch the user context right?
> >
> > Isnt it possible to avoid these patches if do the allocation in another
> > task context instead?
> >
> 
> Sorry, can you please explain what you mean by 'switch the user
> context'. Is there any example in kernel which does something similar?
> 
> Another way is by adding a field 'remote_memcg_to_charge' in
> task_struct and set it before the allocation and in memcontrol.c,
> first check if current->remote_memcg_to_charge is set otherwise use
> the memcg of current. Also if we provide a wrapper to do that for the
> user, there will be a lot less plumbing.
> 
> Please let me know if you prefer this approach.

That would be a lot simpler.  Passing function arguments via
task_struct is a bit dirty but is sometimes sooo effective.  You
should've seen how much mess task_struct.journal_info avoided!  And
reclaim_state.

And one always wonders whether we should do a local save/restore before
modifying the task_struct field, so it nests.

What do others think?


Maybe we can rename task_struct.reclaim_state to `struct task_mm_state
*task_mm_state", add remote_memcg_to_charge to struct task_mm_state and
avoid bloating the task_struct?