On 2011-02-10 14:19, Avi Kivity wrote: > On 02/10/2011 03:14 PM, Jan Kiszka wrote: >> On 2011-02-10 13:57, Avi Kivity wrote: >>> On 02/10/2011 02:56 PM, Avi Kivity wrote: >>>>> What's the benefit? The downside is a bit more complexity as you need an >>>>> additional callback handler. >>>> >>>> >>>> synchronize_rcu() can be very slow (its a systemwide operation), and >>>> mmu_shrink() can be called often on a loaded system. >>>> >>> >>> In fact this just shows that vm_list is not a good candidate for rcu; >>> rcu is useful where most operations are reads, but if we discount stats, >>> most operations on vm_list are going to be writes. >> >> Accept for mmu_shrink, which is write but not delete, thus works without >> that slow synchronize_rcu. > > I don't really see how you can implement list_move_rcu(), it has to be > atomic or other users will see a partial vm_list. Right, even if we synchronized that step cleanly, rcu-protected users could miss the moving vm during concurrent list walks. What about using a separate mutex for protecting vm_list instead? Unless I missed some detail, mmu_shrink should allow blocking. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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
