Hi. On Fri, 2007-04-27 at 07:52 +0300, Pekka J Enberg wrote: > On Thu, 2007-04-26 at 09:56 -0700, Linus Torvalds wrote: > > > which will map in the snapshot, return the mapped address and the size > > > (and if you want to support snapshots > 4GB, be my guest, but I > > > suspect > > > you're actually *better* off just admitting that if you cannot shrink > > > the snapshot to less than 32 bits, it's not worth doing) > > On Fri, 27 Apr 2007, Nigel Cunningham wrote: > > That inherently limits the image to half of available ram (you need > > somewhere to store the snapshot), so you won't get the full image you > > express interest in below. > > It doesn't. We can make the userspace mapped pages copy-on-write. As long > as the userspace makes sure there's not much activity during > snapshot/shutdown, we will be fine. What we probably do need to copy is > kernel pages.
COW is a possibility, but I understood (perhaps wrongly) that Linus was thinking of a single syscall or such like to prepare the snapshot. If you're going to start doing things like this, won't that mean you'd then have to update/redo the snapshot or somehow nullify the effect of anything the programs does so that doing it again after the snapshot is restored doesn't cause problems? I was going to leave it at that and press send, but perhaps that wouldn't be wise. I feel I should also ask what you're thinking of as a means of making sure userspace doesn't do much activity. Thanks for your labours! Regards, Nigel
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