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 10:00:51 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     David Hildenbrand <david@...hat.com>,
        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 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.

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.