linux-kernel - Re: Thoughts on simple scanner approach for free page hinting

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Message-ID: <20190408203541-mutt-send-email-mst@kernel.org>
Date:   Mon, 8 Apr 2019 22:44:25 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Nitesh Narayan Lal <nitesh@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Paolo Bonzini <pbonzini@...hat.com>, lcapitulino@...hat.com,
        pagupta@...hat.com, wei.w.wang@...el.com,
        Yang Zhang <yang.zhang.wz@...il.com>,
        Rik van Riel <riel@...riel.com>, dodgen@...gle.com,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        dhildenb@...hat.com, Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: Thoughts on simple scanner approach for free page hinting

On Fri, Apr 05, 2019 at 05:09:45PM -0700, Alexander Duyck wrote:
> In addition we will need some way to identify which pages have been
> hinted on and which have not. The way I believe easiest to do this
> would be to overload the PageType value so that we could essentially
> have two values for "Buddy" pages. We would have our standard "Buddy"
> pages, and "Buddy" pages that also have the "Offline" value set in the
> PageType field. Tracking the Online vs Offline pages this way would
> actually allow us to do this with almost no overhead as the mapcount
> value is already being reset to clear the "Buddy" flag so adding a
> "Offline" flag to this clearing should come at no additional cost.

It bothers me a bit that this doesn't scale to multiple hint types
if we ever need them. Would it be better to have two
free lists: hinted and non-hinted one?


-- 
MST