linux-kernel - Re: [PATCH v25 1/2 RESEND] mm: support reporting free page blocks

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Message-Id: <20180125144124.7e9f6e2156b1b940b07aecfc@linux-foundation.org>
Date:   Thu, 25 Jan 2018 14:41:24 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Wei Wang <wei.w.wang@...el.com>
Cc:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, mst@...hat.com, mhocko@...nel.org,
        pbonzini@...hat.com, liliang.opensource@...il.com,
        yang.zhang.wz@...il.com, quan.xu0@...il.com, nilal@...hat.com,
        riel@...hat.com
Subject: Re: [PATCH v25 1/2 RESEND] mm: support reporting free page blocks

On Thu, 25 Jan 2018 17:38:27 +0800 Wei Wang <wei.w.wang@...el.com> wrote:

> This patch adds support to walk through the free page blocks in the
> system and report them via a callback function. Some page blocks may
> leave the free list after zone->lock is released, so it is the caller's
> responsibility to either detect or prevent the use of such pages.
> 
> One use example of this patch is to accelerate live migration by skipping
> the transfer of free pages reported from the guest. A popular method used
> by the hypervisor to track which part of memory is written during live
> migration is to write-protect all the guest memory. So, those pages that
> are reported as free pages but are written after the report function
> returns will be captured by the hypervisor, and they will be added to the
> next round of memory transfer.

It would be useful if we had some quantitative testing results, so we
can see the real-world benefits from this change?