> > > > I am now working on how to benefit post-copy by skipping the free > > > > pages, and I remember you have said we should let the destination > > > > know the info of free pages so as to avoid request the free pages > > > > from the > > > source. > > > > > > > > We have two solutions: > > > > > > > > a. send the migration dirty page bitmap to destination before post > > > > copy start, so the destination can decide whether to request the > > > > pages or place zero pages by checking the migration dirty page > > > > bitmap. The advantage is that we can avoid sending the free pages. > > > > the disadvantage is that we have to send extra data to destination. > > > > > > > > b. Check the page request on the source side, if it's not a dirty > > > > page, send a zero page header to the destination. > > > > > > > > What's your opinion about them? > > > > > > > > Liang > > > > > > > > > > Both are ad-hoc solutions imho. > > > > > > c. put the bitmap in a ramblock, check it on destination before > > > requesting pages. > > > > > > This way it's migrated on-demand. > > > > > Hi MST, > > > > I think you mean putting the free page bitmap in a ramblock. Right? > > If some of the free pages become dirty after updating the free page > > bitmap, and these pages are discarded by destination, how can we > > distinguish these discarded pages with the free pages? > > > > Could you elaborate how it works? > > > > Thanks! > > Liang > > Maybe I'm confused - IIUC it's postcopy so VM is running on destination, if > page is dirty it was modified there so we don't need to get it from source. > The current post-copy is implemented as pre-copy plus post-copy, there is a stage that the source told the destination to discard the newly dirty pages before vm start to run on destination. I don't think the free page bitmap will help, we need a dirty page bitmap. The dirty page bitmap should not be put in a ramblock, it does not belong to guest. > But really I agree with David here - at step 1 just ignore post-copy, don't > special-case it, even if it becomes slower with your patch. > Think about it later. > Yes, we can simply ignore the free page if post-copy is enabled. Think about it now will make my work easier :) Thanks! Liang > > > > > > > -- > > > MST > > > -- -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
