Just wanted to say thank you for all of the replies... I will test the pagecache and swappiness parameters to see if they can help me. One more thing I would like to ask... In the past we were all talking about cmm-2 and how great it will be that the cache pages will be marked so that z/VM will recognize them. What happened there? Why isn't that available?
Thanks again, Offer Baruch -----Original Message----- From: Linux on 390 Port [mailto:[email protected]] On Behalf Of Alan Cox Sent: Friday, February 12, 2010 1:50 PM To: [email protected] Subject: Re: Linux file system cache On Fri, 12 Feb 2010 16:56:48 +1000 Shane <[email protected]> wrote: > For those interested, here is the discussion on lkml; > http://lkml.org/lkml/2007/1/23/263 > > It's not like it was rejected without any consideration. > In the time I have been (occasionally) lurking lkml, this has been > raised more than once - and got nowhere. > Maybe Alan Cox will offer a comment. The kernel takes the view that free memory is waste memory. The page cache therefore isn't turned into free space as pages are not needed but instead the vm makes sure most of it is 'clean' - ie correct on disk. That means that when pages are needed the vm simply tosses stuff out of the page cache. If you suddenely need a lot of memory then all the unused bits in the page cache get tossed. When measuring it also remember that a lot of stuff in the page cache will be things like undirtied pages of executables you are running, mapped files etc - it's not a simple buffering system for disk writes. Virtualisers normally interact with all this by having drivers in each guest that allocate memory in respose to global hypervisor managed demand and peeking at local behaviour. The allocated pages are then removed from the guest and given by the hypervisor to another guest and vice versa as demand shifts. Effectively the total pages available is rather lower than the guests perceive. Alan ---------------------------------------------------------------------- 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 No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.733 / Virus Database: 271.1.1/2686 - Release Date: 02/13/10 21:35:00 No virus found in this outgoing message. Checked by AVG - www.avg.com Version: 9.0.733 / Virus Database: 271.1.1/2686 - Release Date: 02/13/10 21:35:00 ---------------------------------------------------------------------- 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
