Re: [PATCH 0/5] Swap Migration V5: Overview

[KAMEZAWA Hiroyuki]

Andrew Morton wrote:
> Christoph Lameter <clameter@xxxxxxx> wrote:
>
> > This is a patchset intended to introduce page migration into the kernel
> > through a simple implementation of swap based page migration.
> > The aim is to be minimally intrusive in order to have some hopes for inclusion
> > into 2.6.15. A separate direct page migration patch is being developed that
> > applies on top of this patch. The direct migration patch is being discussed on
> > <lhms-devel@xxxxxxxxxxxxxxxxxxxxx>.
>
>
> I remain concerned that it hasn't been demonstrated that the infrastructure
> which this patch provides will be adequate for all future applications -
> especially memory hot-remove.
> So I'll queue this up for -mm, but I think we need to see an entire
> hot-remove implementation based on this, and have all the interested
> parties signed up to it before we can start moving the infrastructure into
> mainline.
>

It looks Christoph didn't use (direct)memory migration core in this set,
so memory-hotremove will not be affected by this.

At the first look, memory hotplugger will just replace swap_page()
with migrate_onepage().

Comparing swap-based migration and memory hotremove, memory hotremove
has to support wider kinds of pages other than anon, file-cache
swap-cache, mlocked() page used by direct I/O, HugeTLB pages and achieve
close to 100% guaranntee. Ignoring the fact migration and hotremove will
share the code, what they have to do is very different.

swap-based approach looks just intend to do process migration and
it itself looks not bad.

I think your point is that hotremove and migration will share some amounts of codes.
We are now discussing *direct* page migration and will share codes for anon pages.
It is being discussed in -lhms. We'd like to create good one.

Thanks,
-- KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

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