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
