Re: shared memory usage tool - exmap

[Soeren Sandmann <sandmann daimi au dk>]

John Berthels <jjberthels gmail com> writes:

> I guess I'm saying it may be worth a second look :-)

Well, it locks up my system hard (2.6.12-1.1446_FC5, ie. Fedora
rawhide from a while back which might explain it), but if it does what
you say it does it would certainly be a very useful tool to have.

Since I haven't seen it running, this may be irrelevant, but have you
considered the approach of having the kernel module export an
interface that would map any given pfn to a list of all its mappings?
This would give an overview of how the physical RAM is actually shared
by applications, rather than showing how an individual application is
using physical RAM. (I think both ways of looking at memory would be
useful).

For a given vma it might even be possible to tell whether the page had
actually been added to the pagetable, or whether it was in the
mapping, but not present in the pagetable.  (I am possibly revealing
my limited understanding of virtual memory here).

Having that information would allow us to do things like quantify the
cost of having applications still using GtkCList: if only one
application used GtkCList, you'd see the physical GtkCList pages
mapped into all gtk2 applications, but only present in the pagetable
for the CList-using application. Same thing for other rarely-used
code, of course.


Soeren