linux-kernel - Re: [PATCH RESEND] mm: don't zero ballooned pages

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Message-ID: <8b862c93-1a9f-9247-8401-5092cc35a857@redhat.com>
Date:   Mon, 7 Aug 2017 11:37:26 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Wei Wang <wei.w.wang@...el.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, virtualization@...ts.linux-foundation.org,
        mst@...hat.com, zhenwei.pi@...runcloud.com, dave.hansen@...el.com,
        akpm@...ux-foundation.org, mawilcox@...rosoft.com,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH RESEND] mm: don't zero ballooned pages

> Maybe it is my absolute lack of familiarity with what the host actually
> does with balloon pages but I fail to see why the above matters at all.
> ksm will not try to merge sub page units (4k for hugetlb or a large base
> page). And if you need to hide the guest contents then the host can
> clear the respective subpage just fine. So could you be more explicit
> why MADV_DONTNEED matters at all? Also does any host actually share sub
> pages between different guests? This sounds like a bad idea to me in
> general.
> 

Okay, I think I got the issue wrong. I thought that the original patch
tried to also fix a corner case where the guest would assume that it
would get supplied zero pages afterwards. Please ignore the noise. :)

-- 

Thanks,

David