Re: [RFC PATCH v5 6/8] drivers: vmware: balloon - report inflated memory

[Alexander Atanasov]

On 21.10.22 9:50, Nadav Amit wrote:
> On Oct 19, 2022, at 12:56 PM, Alexander Atanasov <alexander.atanasov@xxxxxxxxxxxxx> wrote:
>
> > Update the inflated memory in the mm core on change.
> >
> > Signed-off-by: Alexander Atanasov <alexander.atanasov@xxxxxxxxxxxxx>
> > ---
> > drivers/misc/vmw_balloon.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/misc/vmw_balloon.c b/drivers/misc/vmw_balloon.c
> > index 91d4d2a285c5..3bfd845898f5 100644
> > --- a/drivers/misc/vmw_balloon.c
> > +++ b/drivers/misc/vmw_balloon.c
> > @@ -1507,6 +1507,7 @@ static void vmballoon_work(struct work_struct *work)
> > 	queue_delayed_work(system_freezable_wq,
> > 			   dwork, round_jiffies_relative(HZ));
> >
> > +	balloon_set_inflated_free(atomic64_read(&b->size) << 2);
> > }
>
> I don’t like it in general (I think that something like that should go into
> some common infra).

My goal is to create that infra, sure there is a place for improvement.
I think of it as a commit point so plugging it into something existing 
does not fit or at least i don't see how.

> But more concretely there are at least 2 problems here. First, queueing the
> work should come last. Second, there are other places that change the
> balloon size (e.g., vmballoon_reset()), which are not handled by this patch.
>
> If you added calls to balloon_set_inflated_free() from these places, you can
> get races while calling balloon_set_inflated_free() and the last value that
> would be latched would be the wrong one. I don’t see anything in the logic
> or comments that clarify how something like that should be resolved.


Ok,I will move it before the enqueue call.
But are you sure about this the reset?
vmballoon_reset(...) is called only from vmballoon_work(...) which does 
the update ? what i am missing?


--
Regards,
Alexander Atanasov