linux-kernel - Re: [RFC PATCH v5 6/8] drivers: vmware: balloon

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Message-ID: <627d2c7f-8ba0-2910-a98d-ef42b9dd5ade@virtuozzo.com>
Date:   Fri, 21 Oct 2022 10:25:05 +0300
From:   Alexander Atanasov <alexander.atanasov@...tuozzo.com>
To:     Nadav Amit <namit@...are.com>
Cc:     Pv-drivers <Pv-drivers@...are.com>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "kernel@...nvz.org" <kernel@...nvz.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v5 6/8] drivers: vmware: balloon - report inflated
 memory

On 21.10.22 9:50, Nadav Amit wrote:
> On Oct 19, 2022, at 12:56 PM, Alexander Atanasov <alexander.atanasov@...tuozzo.com> wrote:
> 
>> Update the inflated memory in the mm core on change.
>>
>> Signed-off-by: Alexander Atanasov <alexander.atanasov@...tuozzo.com>
>> ---
>> 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