Re: [PATCH 00/10] Introduce guestmemfs: persistent in-memory filesystem

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On Mon, Aug 5, 2024 at 4:35 PM Theodore Ts'o <tytso@xxxxxxx> wrote:
> On Mon, Aug 05, 2024 at 11:32:35AM +0200, James Gowans wrote:
> > Guestmemfs implements preservation acrosss kexec by carving out a
> > large contiguous block of host system RAM early in boot which is
> > then used as the data for the guestmemfs files.
>
> Also, the VMM update process is not a common case thing, so we don't
> need to optimize for performance.  If we need to temporarily use
> swap/zswap to allocate memory at VMM update time, and if the pages
> aren't contiguous when they are copied out before doing the VMM
> update

I'm not sure I understand, where would this temporary allocation happen?

> that might be very well worth the vast of of memory needed to
> pay for reserving memory on the host for the VMM update that only
> might happen once every few days/weeks/months (depending on whether
> you are doing update just for high severity security fixes, or for
> random VMM updates).
>
> Even if you are updating the VMM every few days, it still doesn't seem
> that permanently reserving contiguous memory on the host can be
> justified from a TCO perspective.

As far as I understand, this is intended for use in systems that do
not do anything except hosting VMs, where anyway you'd devote 90%+ of
host memory to hugetlbfs gigapages.

Paolo






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