> From: Andrew Miehs [mailto:[EMAIL PROTECTED] > Subject: Re: [OT]Re: Is better one or more Tomcat instances > per machine > > Your kernel, and the things which are doing your process > switching need somewhere to run - if you switch them out > of your 4GB of virtual address space, how are they ever > meant to 'come back to life' on the next context switch.
In IA32, it is theoretically possible to run every user process with a 4 GB local descriptor table, and when a kernel service is required, the hardware switches to the global descriptor table due to the interrupt; the global one maps the kernel space. Once in kernel mode, the OS code can juggle the segment and page tables any way it sees fit. I don't know if anyone actually does run with a 4 GB user process space; most use a split in the virtual space to avoid the above juggling. > Didn't the reason for choosing this size have something to do with > the memory required by the PCI slots, etc? Not sure what you mean by "this size", since we're discussing lots of them here. There is considerable address space history to look back on, starting with the original IBM PC running in what's now called x86 real mode. Many of the IA32 architecture aspects have evolved with compatibility and migration in mind, so it's not what you'd design from scratch. - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. --------------------------------------------------------------------- To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
