On Wed, Feb 27, 2008 at 2:59 PM, Martin Schwidefsky <[EMAIL PROTECTED]> wrote:
> The EX_TABLE entry will take care of the fault. As far as I can tell > Heikos patch is fine. Yes, and I see now that this is only in the __init part so it should not bother me. > > PS I did read that Brian Wade's experiments were done with cmma=on and > > use the CP settings to enable / disable the feature. When my > > assumptions about the implementation are correct, then that was indeed > > the right way to do it. But it does not reveal what will happen to > > customers who end up with a mix of penguins. > > This would be an interesting experiment. The difference between cmma=on > and cmma=off for a page cache page that has been paged-out by z/VM is > not big. If a guest accesses such a page with cmma=off the z/VM system > will initiate an i/o to get the page and deliver a pfault interrupt to > the guest so that the guest can schedule another process. If a guest > uses cmma=on it will get a discard fault on access of a paged-out page. > In this case it is Linux that initiates the i/o. The process will have > to wait for page and another process is scheduled. Our first assumption was that if some of the guests play the game nice with cmma=on telling CP what pages they can afford to miss, they would be very easy target to take pages from. Much easier than guests that are not co-operative and CP must assume their entire working set is stable. It did not turn out to work that way. The situation where CP assumes the guest is co-operative (because it issued an ESSA) but Linux decides not to flag pages would make the entire virtual machine as stable (I assume). I understand the Linux view on this. But apart from that, I believe it would influence which pages CP takes away when it can pick. Now I often see CP take pages that are paged out already, which is not good. If the cmma stuff does not change the z/VM demand scan then I think it's a missed opportunity. Rob -- Rob van der Heij Velocity Software, Inc http://velocitysoftware.com/ ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
