lkml.org 
[lkml]   [2002]   [Jan]   [9]   [last100]   RSS Feed
Views: [more markup]   [less markup]   [headers]   [forward]  
 
Messages in this thread
/
SubjectRe: can we make anonymous memory non-EXECUTABLE?
FromDoug McNaught <>
Date09 Jan 2002 14:47:32 -0500
Rob Landley <landley@trommello.org> writes:

> Glibc does mmap instead of brk because theoretically brk can leave wasted 
> memory between fragments, although apparently nobody's ever seen more than 
> 10% waste in a live program, and the speed penality of taking a soft page 
> fault at access time to muck about with the page tables is a LOT bigger than 
> 10%...

The other reason glibc uses mmap() is because your shared libraries
are (usually) mapped smack dab in the middle of your address space.
brk() assumes a contiguous heap, so when it hits your libraries, it
has to stop, even if there is a gig of VM above the libs.  mmap() can
give you an arbitrary chunk of the address space, so glibc uses it for
'large' allocations.

-Doug
-- 
Let us cross over the river, and rest under the shade of the trees.
   --T. J. Jackson, 1863
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 12:15    [W:0.224 / U:0.160 seconds]
©2003-2008 Jasper Spaans