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Message-ID: <1497977049.20270.100.camel@redhat.com>
Subject: Re: [PATCH v11 4/6] mm: function to offer a page block on the free
 list
From: Rik van Riel <riel@redhat.com>
To: Dave Hansen <dave.hansen@intel.com>, Wei Wang <wei.w.wang@intel.com>,
        linux-kernel@vger.kernel.org, qemu-devel@nongnu.org,
        virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
        linux-mm@kvack.org, mst@redhat.com, david@redhat.com,
        cornelia.huck@de.ibm.com, akpm@linux-foundation.org,
        mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com,
        pbonzini@redhat.com, liliang.opensource@gmail.com
Cc: Nitesh Narayan Lal <nilal@redhat.com>
Date: Tue, 20 Jun 2017 12:44:09 -0400
In-Reply-To: <b92af473-f00e-b956-ea97-eb4626601789@intel.com>
References: <1497004901-30593-1-git-send-email-wei.w.wang@intel.com>
         <1497004901-30593-5-git-send-email-wei.w.wang@intel.com>
         <b92af473-f00e-b956-ea97-eb4626601789@intel.com>
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On Mon, 2017-06-12 at 07:10 -0700, Dave Hansen wrote:

> The hypervisor is going to throw away the contents of these pages,
> right?=C2=A0=C2=A0As soon as the spinlock is released, someone can alloca=
te a
> page, and put good data in it.=C2=A0=C2=A0What keeps the hypervisor from
> throwing
> away good data?

That looks like it may be the wrong API, then?

We already have hooks called arch_free_page and
arch_alloc_page in the VM, which are called when
pages are freed, and allocated, respectively.

Nitesh Lal (on the CC list) is working on a way
to efficiently batch recently freed pages for
free page hinting to the hypervisor.

If that is done efficiently enough (eg. with
MADV_FREE on the hypervisor side for lazy freeing,
and lazy later re-use of the pages), do we still
need the harder to use batch interface from this
patch?

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