linux-kernel - Re: [PATCH v1 2/2] Drivers: virtio: balloon: Report inflated memory

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Date:   Tue, 16 Aug 2022 10:50:07 +0300
From:   Alexander Atanasov <alexander.atanasov@...tuozzo.com>
To:     Nadav Amit <namit@...are.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "kernel@...nvz.org" <kernel@...nvz.org>,
        Wei Liu <wei.liu@...nel.org>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Pv-drivers <Pv-drivers@...are.com>
Subject: Re: [PATCH v1 2/2] Drivers: virtio: balloon: Report inflated memory

On 15.08.22 19:05, Nadav Amit wrote:
> On Aug 15, 2022, at 5:52 AM, Alexander Atanasov <alexander.atanasov@...tuozzo.com> wrote:
> 
>> If it is going to be a place for generic logic may be it should be
>> renamed to balloon_common.[ch] ?
>>
>>> as possible. I made the effort to reuse this infrastructure (which is now
>>> used by both VMware and virtio), and would prefer to share as much code as
>>> possible.
>>>
>>> For instance, I would appreciate if the update upon inflate would go into
>>> balloon_page_list_enqueue() and balloon_page_enqueue(). VMware's 2MB pages
>>> logic is not shared, so it would require a change that is specific for
>>> VMware code.
>>
>> I looked at the code and i do not see how i can reuse it since
>> BALLOON_COMPACTION can be disabled and as you say even for VMWare it
>> would require updates on other places. Looks like if i do so i would
>> have to handle update from each driver for both cases. I think it is
>> better to clearly mark the spots when drivers do their internal
>> recalculations and report to the core. I see only VMWare is using
>> balloon_page_list_enqueue , virtio balloon is using only migration and
>> i don't see how to hook it there - i haven't checked the rest of the
>> balloons but i guess it would be similiar . I agree it is a good to have
>> a common place for such logic but it might be better of for a separate
>> work in the future.
> 
> Fine. I would live with whatever you do and if needed change it later.


- balloon_page_list_enqueue and balloon_page_enqueue are called under locks.
- they work page by page
- different page sizes different hypervisors
- pages to bytes conversion again different page sizes

I will put the new code in balloon_common but i can not reuse what you 
propose for the reasons above.

-- 
Regards,
Alexander Atanasov