Re: [PATCH 2 of 4] x86/mm: Allow to not sleep on mem event ring

[Tim Deegan <tim@xen.org>]

At 22:57 -0500 on 15 Feb (1329346625), Andres Lagar-Cavilla wrote:
>  xen/arch/x86/mm/mem_event.c     |   5 +++--
>  xen/include/asm-x86/mem_event.h |  30 +++++++++++++++++++++++++-----
>  2 files changed, 28 insertions(+), 7 deletions(-)
> 
> 
> Under extreme congestion conditions, generating a mem event may put the vcpu to
> sleep on a wait queue if the ring is full. This is generally desirable, although
> fairly convoluted to work with, since sleeping on a wait queue requires a
> non-atomic context (i.e. no locks held).
> 
> Introduce an allow_sleep flag to make this optional. The API remains such that
> all current callers set allow_sleep to true and thus will sleep if necessary.
> 
> The end-use is for cases in which loss of guest mem events is tolerable. One
> such consumer to be added later is the unsharing code under ENOMEM conditions.
> 
> Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
> Signed-off-by: Adin Scannell <adin@scannell.ca>

Hmm.  This interface is getting a bit twisty now, but assuming the
patches that use it are OK, then Ack.

Tim.