From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jacob Gorm Hansen Subject: Re: copy on write memory Date: Mon, 22 Nov 2004 13:42:37 +0100 Message-ID: <41A1DEBD.6060002@diku.dk> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: xen-devel-admin@lists.sourceforge.net Errors-To: xen-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , List-Archive: To: Keir Fraser Cc: Xen-devel@lists.sourceforge.net List-Id: xen-devel@lists.xenproject.org Keir Fraser wrote: > > Well, you also can over-commit on stuff that is read-only and fault in > on demand, just as you can demand-CoW writable stuff e.g., no need to > have all of kernel or glibc in memory all the time -- only hot parts > of both will be in use by the system at any time. > > i.e., > 1. There is fault in from no page -> shareable page on read accesses. > 2. There is fault from shareable page -> shareable page + exclusive > page on write accesses. > Both of these require extra allocation of memory. But I will need some external service to give them to me right when I need them, or I may run into the 'paged-the-pager' problem and die? >>Perhaps this should just be a one-way street, you give up pages to be >>nice to others (and get cheaper hosting or whatever kind of reward you >>can think of in return), and then you lose the right to write to them >>for good. Should you need more writable pages, you will have to re-grow >>your reservation, and if that fails you will need to flush some slabs or >>buffer caches or or page stuff to disk or whatever you do in Linux when >>you have memory pressure. Ultimately you may want to migrate to a less >>loaded machine. > > > It's another way of looking at the problem (end-to-end style I > suppose). Potetntially worth investigating. :-) Perhaps I will have a go at some point. If going in this direction perhaps it will make sense to do this in Xen anyway. Jacob ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/