From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from ds02c00.directory.ray.com (ds02c00.rsc.raytheon.com [147.25.138.118]) by dfw-gate4.raytheon.com (8.11.0.Beta3/8.11.0.Beta3) with ESMTP id f0MFt1Z15362 for ; Mon, 22 Jan 2001 09:55:01 -0600 (CST) Received: from rtshou-ds01.hou.us.ray.com (localhost [127.0.0.1]) by ds02c00.directory.ray.com (8.9.3/8.9.3) with ESMTP id JAA10757 for ; Mon, 22 Jan 2001 09:54:15 -0600 (CST) Subject: Locked memory questions Message-ID: From: Mark_H_Johnson@Raytheon.com Date: Mon, 22 Jan 2001 09:54:49 -0600 MIME-Version: 1.0 Content-type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org Return-Path: To: linux-mm@kvack.org Cc: Stanley_R_Allen-NR@Raytheon.com List-ID: I was surprised by a reference in the latest kernel traffic (http://kt.linuxcare.com/kernel-traffic/latest.epl) to a VM problem with large locked memory regions. I read linux-mm on a daily basis, but didn't see this particular discussion go by. We're looking at deploying a large real time system [hard deadlines, lots of locked memory] and have a few questions based on that discussion... [1] Other than the kernel limit on the amount of locked memory [was 50% in 2.2.x], what should I be aware of when setting up a system with huge amounts of locked memory [say, 75% locked on a 256 to 512 Mbyte machine]? [2] Does it matter that I have several threads that map that memory [from 10 to 50, varies by system]? [3] Does it matter that the target system is a Pentium III or not? [4] Are there any other "known problems" with Linux VM and locked memory? If so, any idea on when they will be fixed? We're looking to go into system testing this summer with delivery in November. [5] Are the algorithms you are considering for fixing page aging, etc. do well with locked memory? [6] Where does it explain when a locked page is put into memory? I had assumed it was done when the mlockall() call was done, but now I'm not so sure. We could put a small hunk of code to walk the address space if needed, but need to know for sure. [7] If I use mlockall(), does it lock the maximum stack size for the thread its called from [or just the current stack extent]? [8] Please confirm - A process with its address space locked is NOT a candidate for swapping. In many ways, I'd like the kernel to ignore the locked memory regions from its analysis for page aging, candidates for swapping, etc. We want to use most of the CPU cycles to run our application, not manage the memory that isn't going anywhere. Thanks. --Mark H Johnson -- 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.eu.org/Linux-MM/