lkml.org 
[lkml]   [2007]   [Apr]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
DateThu, 05 Apr 2007 19:52:09 -0700
FromUlrich Drepper <>
SubjectRe: missing madvise functionality
Nick Piggin wrote:
> Cool. According to my thinking, madvise(MADV_DONTNEED) even in today's
> kernels using down_write(mmap_sem) for MADV_DONTNEED is better than
> mmap/mprotect, which have more fundamental locking requirements, more
> overhead and no benefits (except debugging, I suppose).

It's a tiny bit faster, see

http://people.redhat.com/drepper/dontneed.png

I just ran it once so the graph is not smooth. This is on a UP dual
core machine. Maybe tomorrow I'll turn on the big 4p machine.

I would have to see dramatically different results on the big machine to
make me change the libc code. The reason is that there is a big drawback.

So far, when we allocate a new arena, we allocate address space with
PROT_NONE and only when we need memory the protection is changed to
PROT_READ|PROT_WRITE. This is the advantage of catching wild pointer
accesses.
--
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖

[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2007-04-06 04:55    [from the cache]
©2003-2010