Martin Schwidefsky wrote: > On Wed, 2006-09-13 at 10:45 -0400, Rik van Riel wrote: > >>>But another trouble you have not mentioned is what happens to pages >>>with pending make-volatile that need to and/or have been made stable >>>in the meantime. They too need to be removed from this pending list. >> >>At the time where you walk the set of pages (pagevec?) to make >>volatile, you can check whether the page flags are still right. > > > A make volatile can be done anytime as long as the page is in page > cache. Before a page can be made stable the caller needs to make sure > that one of the conditions that prevent a make volatile becomes true. > So a page in the pending make-volatile array does not have to be removed > because a make stable has been done. It only has to be removed if it > gets freed. > > >>A page that was set to be marked volatile with the hypervisor, >>but later turned stable again would have that indicated in its >>page flags, right? > > > Several page flag bits and some other conditions like "has a mapping" > and "reference count is map count + 1". Most of the checks that need to > be done for make volatile are on page flags. > Interesting.. But don't we have to do some locking on the page to avoid race conditions? A page needs to be consistent between check through __page_discardable and committing to the hypervisor. We could raise the PG_state_change flag for that period.
