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Date:   Mon, 18 Feb 2019 11:49:53 -0500
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     Nitesh Narayan Lal <nitesh@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, pbonzini@redhat.com,
        lcapitulino@redhat.com, pagupta@redhat.com, wei.w.wang@intel.com,
        yang.zhang.wz@gmail.com, riel@surriel.com, dodgen@google.com,
        konrad.wilk@oracle.com, dhildenb@redhat.com, aarcange@redhat.com,
        Alexander Duyck <alexander.duyck@gmail.com>
Subject: Re: [RFC][Patch v8 0/7] KVM: Guest Free Page Hinting
Message-ID: <20190218114601-mutt-send-email-mst@kernel.org>
References: <20190204201854.2328-1-nitesh@redhat.com>
 <af4430fd-0a2c-8f35-b767-3f93fc6db270@redhat.com>
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On Sat, Feb 16, 2019 at 10:40:15AM +0100, David Hildenbrand wrote:
> It would be worth a try. My feeling is that a synchronous report after
> e.g. 512 frees should be acceptable, as it seems to be acceptable on
> s390x. (basically always enabled, nobody complains).

What slips under the radar on an arch like s390 might
raise issues for a popular arch like x86. My fear would be
if it's only a problem e.g. for realtime. Then you get
a condition that's very hard to trigger and affects
worst case latencies.

But really what business has something that is supposedly
an optimization blocking a VCPU? We are just freeing up
lots of memory why is it a good idea to slow that
process down?

-- 
MST