linux-kernel - Re: [PATCH v14 3/6] mm: Introduce Reported pages

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Date:   Fri, 29 Nov 2019 11:25:59 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        kvm list <kvm@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Yang Zhang <yang.zhang.wz@...il.com>,
        Nitesh Narayan Lal <nitesh@...hat.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        David Hildenbrand <david@...hat.com>,
        Pankaj Gupta <pagupta@...hat.com>,
        Rik van Riel <riel@...riel.com>, lcapitulino@...hat.com,
        Dave Hansen <dave.hansen@...el.com>,
        "Wang, Wei W" <wei.w.wang@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v14 3/6] mm: Introduce Reported pages

On Thu, Nov 28, 2019 at 1:22 AM Mel Gorman <mgorman@...hsingularity.net> wrote:
>
> On Wed, Nov 27, 2019 at 01:55:02PM -0800, Alexander Duyck wrote:

< snip >

> > >
> > > Which in itself could be an optimisation patch. Maybe it'll be enough that
> > > keeping track of the count is not worthwhile. Either way, the separate
> > > patch could have supporting data on how much it improves the speed of
> > > reporting pages so it can be compared to any other optimisation that
> > > may be proposed. Supporting data would also help make the case that any
> > > complexity introduced by the optimisation is worthwhile.
> >
> > I'll see what I can do to break this apart. I'm just not a fan of redoing
> > the work multiple times so that I can have a non-optimized version versus
> > an optimized one.
> >
>
> While I understand that, right now the optimisations are blocking the
> feature itself which is also not a situation you want to be in.

I'll see what I can do. I can probably replace the reference count and
zone flags with an atomic state in the prdev that cycles between
inactive, requested, and active. With that I can at least guarantee
that we shouldn't have any races that result in us missing freed
pages. The only downside is that I have to keep a boolean in the
__free_one_page call so that when we free back the reported pages we
don't retrigger the reporting and cause an infinite loop.