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

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Date:   Tue, 25 Jun 2019 20:12:43 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Alexander Duyck <alexander.duyck@...il.com>,
        Dave Hansen <dave.hansen@...el.com>
Cc:     Nitesh Narayan Lal <nitesh@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yang Zhang <yang.zhang.wz@...il.com>, pagupta@...hat.com,
        Rik van Riel <riel@...riel.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        lcapitulino@...hat.com, wei.w.wang@...el.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>, dan.j.williams@...el.com,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Subject: Re: [PATCH v1 0/6] mm / virtio: Provide support for paravirtual waste
 page treatment

On 25.06.19 19:00, Alexander Duyck wrote:
> On Tue, Jun 25, 2019 at 7:10 AM Dave Hansen <dave.hansen@...el.com> wrote:
>>
>> On 6/25/19 12:42 AM, David Hildenbrand wrote:
>>> On 20.06.19 00:32, Alexander Duyck wrote:
>>> 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)
>>
>> It's a wee bit too cute for my taste as well.  I could probably live
>> with it in the data structures, but having it show up out in places like
>> Kconfig and filenames goes too far.
>>
>> For instance, someone seeing memory_aeration.c will have no concept
>> what's in the file.  Could we call it something like memory_paravirt.c?
>>  Or even mm/paravirt.c.
> 
> Well I couldn't come up with a better explanation of what this was
> doing, also I wanted to avoid mentioning hinting specifically because
> there have already been a few series that have been committed upstream
> that reference this for slightly different purposes such as the one by
> Wei Wang that was doing free memory tracking for migration purposes,
> https://lkml.org/lkml/2018/7/10/211.

That one we referred to rather as "free page reporting".

> 
> Basically what we are doing is inflating the memory size we can report
> by inserting voids into the free memory areas. In my mind that matches
> up very well with what "aeration" is. It is similar to balloon in
> functionality, however instead of inflating the balloon we are
> inflating the free_list for higher order free areas by creating voids
> where the madvised pages were.
> 
>> Could you talk for a minute about why the straightforward naming like
>> "hinted/unhinted" wasn't used?  Is there something else we could ever
>> use this infrastructure for that is not related to paravirtualized free
>> page hinting?
> 
> I was hoping there might be something in the future that could use the
> infrastructure if it needed to go through and sort out used versus
> unused memory. The way things are designed right now for instance
> there is only really a define that is limiting the lowest order pages
> that are processed. So if we wanted to use this for another purpose we
> could replace the AERATOR_MIN_ORDER define with something that is
> specific to that use case.


I'd still vote to call this "hinting" in some form. Whenever a new use
case eventually pops up, we could generalize this approach. But well,
that's just my opinion :)


-- 

Thanks,

David / dhildenb