linux-kernel - Re: [PATCH v1 0/6] mm / virtio: Provide support for paravirtual waste page treatment

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Date:   Wed, 26 Jun 2019 11:12:35 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Christophe de Dinechin <dinechin@...hat.com>
Cc:     Alexander Duyck <alexander.duyck@...il.com>, nitesh@...hat.com,
        kvm@...r.kernel.org, mst@...hat.com, dave.hansen@...el.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, yang.zhang.wz@...il.com,
        pagupta@...hat.com, riel@...riel.com, konrad.wilk@...cle.com,
        lcapitulino@...hat.com, wei.w.wang@...el.com, aarcange@...hat.com,
        pbonzini@...hat.com, dan.j.williams@...el.com,
        alexander.h.duyck@...ux.intel.com
Subject: Re: [PATCH v1 0/6] mm / virtio: Provide support for paravirtual waste
 page treatment

On 26.06.19 11:01, Christophe de Dinechin wrote:
> 
> David Hildenbrand writes:
> 
>> On 20.06.19 00:32, Alexander Duyck wrote:
>>> This series provides an asynchronous means of hinting to a hypervisor
>>> that a guest page is no longer in use and can have the data associated
>>> with it dropped. To do this I have implemented functionality that allows
>>> for what I am referring to as waste page treatment.
>>>
>>> I have based many of the terms and functionality off of waste water
>>> treatment, the idea for the similarity occurred to me after I had reached
>>> the point of referring to the hints as "bubbles", as the hints used the
>>> same approach as the balloon functionality but would disappear if they
>>> were touched, as a result I started to think of the virtio device as an
>>> aerator. The general idea with all of this is that the guest should be
>>> treating the unused pages so that when they end up heading "downstream"
>>> to either another guest, or back at the host they will not need to be
>>> written to swap.
>>>
>>> When the number of "dirty" pages in a given free_area exceeds our high
>>> water mark, which is currently 32, we will schedule the aeration task to
>>> start going through and scrubbing the zone. While the scrubbing is taking
>>> place a boundary will be defined that we use to seperate the "aerated"
>>> pages from the "dirty" ones. We use the ZONE_AERATION_ACTIVE bit to flag
>>> when these boundaries are in place.
>>
>> I still *detest* the terminology, sorry. Can't you come up with a
>> simpler terminology that makes more sense in the context of operating
>> systems and pages we want to hint to the hypervisor? (that is the only
>> use case you are using it for so far)
> 
> FWIW, I thought the terminology made sense, in particular given the analogy
> with the balloon driver. Operating systems in general, and Linux in
> particular, already use tons of analogy-supported terminology. In
> particular, a "waste page treatment" terminology is not very far from
> the very common "garbage collection" or "scrubbing" wordings. I would find
> "hinting" much less specific. for example.
> 
> Usually, the phrases that stick are somewhat unique while providing a
> useful analogy to server as a reminder of what the thing actually
> does. IMHO, it's the case here on both fronts, so I like it.

While something like "waste pages" make sense, "aeration" is far out of
my comfort zone.

An analogy is like a joke. If you have to explain it, it's not that
good. (see, that was a good analogy ;) ).

-- 

Thanks,

David / dhildenb