linux-kernel - Re: [RFC][Patch v9 0/6] KVM: Guest Free Page Hinting

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Date:   Mon, 25 Mar 2019 11:37:22 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Nitesh Narayan Lal <nitesh@...hat.com>
Cc:     Alexander Duyck <alexander.duyck@...il.com>,
        David Hildenbrand <david@...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: [RFC][Patch v9 0/6] KVM: Guest Free Page Hinting

On Mon, Mar 25, 2019 at 10:27:46AM -0400, Nitesh Narayan Lal wrote:
> I performed some experiments to see if the current implementation of
> hinting breaks THP. I used AnonHugePages to track the THP pages
> currently in use and memhog as the guest workload.
> Setup:
> Host Size: 30GB (No swap)
> Guest Size: 15GB
> THP Size: 2MB
> Process: Guest is installed with different kernels to hint different
> granularities(MAX_ORDER - 1, MAX_ORDER - 2 and MAX_ORDER - 3). Memhog 
> 15G is run multiple times in the same guest to see AnonHugePages usage
> in the host.
> 
> Observation:
> There is no THP split for order MAX_ORDER - 1 & MAX_ORDER - 2 whereas
> for hinting granularity MAX_ORDER - 3 THP does split irrespective of
> MADVISE_FREE or MADVISE_DONTNEED.
> -- 
> Regards
> Nitesh
> 

This is on x86 right? So THP is 2M and MAX_ORDER is 8M.
MAX_ORDER - 3 ==> 1M.
Seems to work out.

-- 
MST