From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sat, 22 Oct 2005 14:11:33 -0400 (EDT) From: Rik van Riel Subject: Re: a basic question In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Nitin Gupta Cc: linux-mm@kvack.org List-ID: On Sat, 22 Oct 2005, Nitin Gupta wrote: > - How does processor know that 3GB-4GB is mapped linearly on first 1GB > of memory. Is there a pagetable for this segment mapping it linearly? Yes, there are page tables for this. > - Why isn't it like this - userspace tasks have 4GB virtual address > space and for kernel also a 4GB virtual address space that is linearly > mapped to fist 4GB of memory. With the 4:4 split patch, this is done. However, there is a cost to this approach - every time the system switches from user mode to kernel mode it goes through a context switch. An extra two context swiches on every system call, every interrupt. For most systems the gained space is simply not worth the time overhead. -- All Rights Reversed -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org