On Tue, Nov 26, 2013 at 11:21:37AM +0800, Xiao Guangrong wrote: > On 11/26/2013 02:12 AM, Marcelo Tosatti wrote: > > On Mon, Nov 25, 2013 at 02:29:03PM +0800, Xiao Guangrong wrote: > >>>> Also, there is no guarantee of termination (as long as sptes are > >>>> deleted with the correct timing). BTW, can't see any guarantee of > >>>> termination for rculist nulls either (a writer can race with a lockless > >>>> reader indefinately, restarting the lockless walk every time). > >>> > >>> Hmm, that can be avoided by checking dirty-bitmap before rewalk, > >>> that means, if the dirty-bitmap has been set during lockless > >>> write-protection, > >>> it�s unnecessary to write-protect its sptes. Your idea? > >> This idea is based on the fact that the number of rmap is limited by > >> RMAP_RECYCLE_THRESHOLD. So, in the case of adding new spte into rmap, > >> we can break the rewalk at once, in the case of deleting, we can only > >> rewalk RMAP_RECYCLE_THRESHOLD times. > > > > Please explain in more detail. > > Okay. > > My proposal is like this: > > pte_list_walk_lockless() > { > restart: > > + if (__test_bit(slot->arch.dirty_bitmap, gfn-index)) > + return; > > code-doing-lockless-walking; > ...... > } > > Before do lockless-walking, we check the dirty-bitmap first, if > it is set we can simply skip write-protection for the gfn, that > is the case that new spte is being added into rmap when we lockless > access the rmap.
The dirty bit could be set after the check. > For the case of deleting spte from rmap, the number of entry is limited > by RMAP_RECYCLE_THRESHOLD, that is not endlessly. It can shrink and grow while lockless walk is performed. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html