From 11b74e38761fd04b8ca2bf9a85bb55fbf4d202ea Mon Sep 17 00:00:00 2001 From: Thomas Schwinge Date: Sun, 27 Sep 2009 23:08:39 +0200 Subject: Move Viengoos projects into separate per-project pages. --- .../projects/address_space_management.mdwn | 40 ++++++++++++++++++++++ 1 file changed, 40 insertions(+) create mode 100644 microkernel/viengoos/projects/address_space_management.mdwn (limited to 'microkernel/viengoos/projects/address_space_management.mdwn') diff --git a/microkernel/viengoos/projects/address_space_management.mdwn b/microkernel/viengoos/projects/address_space_management.mdwn new file mode 100644 index 00000000..2d00e4f4 --- /dev/null +++ b/microkernel/viengoos/projects/address_space_management.mdwn @@ -0,0 +1,40 @@ +[[!meta copyright="Copyright © 2008, 2009 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]]."]]"""]] + +[[!tag open_issue_viengoos]] + +In Viengoos, a process's address space is managed entirely in user +space by the process itself. This creates two interesting problems: +dealing with circular dependencies resulting from having to manage the +address space data structures and accessing and manipulating the +address space data structures. + +First, managing the address space requires resources, which in turn +may require address space (e.g., data structures require memory which +require address space, etc.). We currently break this circular +dependency by trying to keep enough resources in reserve that +allocating resources for managing the address space never requires +more resources than are minimally in the reserve. The reserve is +currently chosen in an ad-hoc fashion. It would be nice to determine +it more systematically. Moreover, it would be nice to reduce the +cases in which a reserve is required. This may be possible by +restructuring some of the code. + +Second, the address space data structures are protected using a single +lock. This not only means that only a single thread can be updating +the address space at a time, but that if a thread faults and the +address space is locked, then the process dead locks! It should be +possible to at least walk the address space using lock-free +techniques. This requires updating the address space construction +code such that all addresses remain valid during any given +manipulation. Second, to avoid the mentioned dead-lock problem, we +try to ensure that accessing the data structures will never result in +a fault. This means protecting the stack. An alternative approach is +to use undo buffers. -- cgit v1.2.3