From da95fdb2a18809582eafb656cc61a45d1bdc00fc Mon Sep 17 00:00:00 2001 From: Richard Braun Date: Wed, 11 Mar 2015 19:03:17 +0100 Subject: New GSoC project idea about physical memory management --- .../project_ideas/physical_memory_management.mdwn | 51 ++++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 community/gsoc/project_ideas/physical_memory_management.mdwn diff --git a/community/gsoc/project_ideas/physical_memory_management.mdwn b/community/gsoc/project_ideas/physical_memory_management.mdwn new file mode 100644 index 00000000..c074c3d5 --- /dev/null +++ b/community/gsoc/project_ideas/physical_memory_management.mdwn @@ -0,0 +1,51 @@ +[[!meta copyright="Copyright © 2015 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled +[[GNU Free Documentation License|/fdl]]."]]"""]] + +[[!meta title="Physical memory management"]] + +GNU Mach is currently suffering from severe limitations caused by the way +it manages physical memory. For example, since it requires pages to be mapped +in kernel space in order to be used, the maximum amount of usable physical +memory is currently around 800MB (or 1.8GB is a 2/2 split is set). And +because the page allocator is unable to easily return blocks of contiguous +pages, the kernel has to use virtual memory to provide contiguity. +But the kernel virtual space is separate from the direct mapping of +physical memory, so the larger it is, the less physical pages available. +The size of the kernel space is currently around 200MB, with around 100MB +for kernel objects. This small size prevents the system from achieving +scalability, since a panic occurs when the kernel is unable to allocate +a kernel object such as a port. In addition, the kernel uses mainly tables +to store IPC rights. When a table is full, it is enlarged through a kernel +specific version of realloc(). When a file system starts managing many +files (e.g. because some of their content is cached in physical memory), +these tables can get big enough to make realloc() fail because of +fragmentation. + +The goal of this project is to make as much physical memory available as +possible for both the kernel and applications, by rewriting the page +allocator into a buddy allocator to support contiguous block allocations, +using it directly instead of virtual memory as the backend of the slab +allocator for kernel objects, and, if time allows it, transform IPC right +tables (e.g. into radix trees) and get rid of realloc(). + +This project requires a good understanding of virtual memory (both physical +mappings at the MMU level and virtual mappings at the VM level), and strong +skills in C programming. Note that some work has already been done in the +X15 project about this, and can be reused as a reference. + +Useful links : + + * + + * + + * + +Possible mentors: Richard Braun -- cgit v1.2.3