On 04/22/2012 07:39 PM, Avi Kivity wrote: > On 04/21/2012 05:31 AM, Marcelo Tosatti wrote: >> On Thu, Apr 19, 2012 at 07:26:35PM +0300, Avi Kivity wrote: >>> This patchset simplifies the freeing by RCU of mmu pages. >>> >>> Xiao, I'm sure you thought of always freeing by RCU. Why didn't you choose >>> this way? I saves a couple of atomics in the fast path. >>> >>> Avi Kivity (2): >>> KVM: MMU: Always free shadow pages using RCU >>> KVM: MMU: Recover space used by rcu_head in struct kvm_mmu_page >>> >>> arch/x86/include/asm/kvm_host.h | 9 +++--- >>> arch/x86/kvm/mmu.c | 58 ++++++++------------------------------- >>> 2 files changed, 15 insertions(+), 52 deletions(-) >> >> Check Documentation/RCU/checklist.txt item 8. >> >> a. Keeping a count of the number of data-structure elements >> used by the RCU-protected data structure, including >> those waiting for a grace period to elapse. Enforce a >> limit on this number, stalling updates as needed to allow >> previously deferred frees to complete. Alternatively, >> limit only the number awaiting deferred free rather than >> the total number of elements. >> > > That's true before and after the patch. Currently the amount of memory > that depends on rcu for freeing is unbounded. > > Maybe we should protect the fast path using local_irq_disable() instead > of rcu_read_lock(), like x86 page tables. That means that > kvm_flush_remote_tlbs() needs to ignore OUTSIDE_GUEST_MODE when IPIing > vcpu threads. So, IPI is unconditionally sent, do we need introduce a new MODE (say STOP_SP_FREE) to reduce IPI? -- 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
