53311 - implement nsMemoryImpl::IsLowMemory() predicate for Linux

Status: NEW

(Core :: XPCOM, defect, P3)

Description

[Chris Waterson]

Need to implement this to make memory flusher thread do useful stuff.

Comment 1

[Jonathan Lennox]

There was a thread about this on n.p.m.porkjockeys and .unix.
See the thread "hitting the wall" in .unix;
<news://news.mozilla.org/8nfg5u%24l804%40secnews.netscape.com> and
its follow-ups.

Short summary:
* It's not clear what "Low Memory" means on a multi-user, virtual-memory
machine.  Possibilities include % of virtual memory in use, % of real memory in
use, % of user memory, % of getrlimit settings(), or (on AIX) receipt of the
SIGDANGER signal.

* Once you decide what Low Memory means, determining it portably between various
Unixes is very hard.  Effectively, every Unix system defines its own API for
doing this.

* Some Unix implementations require that a process be setuid or setgid kmem in
order to read the kernel structures giving memory-usage information.

* Examples of programs which do this are top (the classic portable
load-monitoring program, <http://www.groupsys.com/top/>) and libgtop (A more
modern architecture indended for use with GNOME,
<http://www.home-of-linux.org/gnome/libgtop/>).  The former program is not
exactly modular, though, and the latter is under a strict-GPL, so neither is
incorporatable into Mozilla; however, code inspiration should be drawable from
them.

Comment 2

[Chris Waterson]

add embed kw