On Wed, Nov 19, 2014 at 01:01:14PM +0530, Amit Shah wrote: > On (Mon) 17 Nov 2014 [22:08:46], Michael S. Tsirkin wrote: > > At the moment we migrate ROMs which reside in fw cfg, which allows > > changing ROM code at will, and supports migrating largish blocks early, > > with good performance. > > However, we are running into a problem: changing size breaks > > migration every time. > > This already requires somewhat messy compatibility support in > > acpi generation code, and it looks like there'll be more to come. > > > > Rather than try to guess the correct size once and for all, > > this patchset tries to make code future-proof, by > > adding support for resizeable ram blocks. > > > > A (possibly very high) amount of space in ram_addr_t space is reserved > > for each block, but never allocated. > > If incoming block size differs from current size, block is > > reallocated. FW CFG is also notified and updated accordingly. > > > > To simplify things, I didn't add support for resizing > > actual RAM: device RAM such as fw cfg ROMs are never mapped > > into guests directly, so instead I added an API to > > flag device RAM explicitly, and manage them using > > simple alloc/free/realloc > > > > Considering this promises to rid us of worries about ROM size considerations > > once and for all, I thinking about pushing this as a "kind of bugfix" before > > 2.2, so we don't need to maintain more band-aids in 2.3 and on. > > I'd rather wait for 2.3; we've done this for a couple of releases > already, so what's one more. And we're at rc2 already..
Paolo feels the same, and I agree. > > Note: migration stream is unaffected by these patches. > > This makes it possible to enable this functionality > > unconditionally, for all machine types. > > > > In the future, this might be handy for other things, > > such as changing kernels loaded on command line > > across migrations. > > I think that'll be too risky; unless we do S4 before / after > migration to ensure the kernel realises things might be changing > beneath its feet. > > Amit Well - guest never sees the resizing. It happens before we start the VM. So I don't see the issue - could you clarify please? -- MST
