linux-kernel - Re: [RFC][Patch v8 0/7] KVM: Guest Free Page Hinting

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Message-ID: <20190218114601-mutt-send-email-mst@kernel.org>
Date:   Mon, 18 Feb 2019 11:49:53 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Nitesh Narayan Lal <nitesh@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        lcapitulino@...hat.com, pagupta@...hat.com, wei.w.wang@...el.com,
        yang.zhang.wz@...il.com, riel@...riel.com, dodgen@...gle.com,
        konrad.wilk@...cle.com, dhildenb@...hat.com, aarcange@...hat.com,
        Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [RFC][Patch v8 0/7] KVM: Guest Free Page Hinting

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