Re: 2.5.64-mm6

[Andrew Morton]

Andi Kleen <[e-mail]> wrote:
>
> Andrew Morton <[e-mail]> writes:
> 
> 
> >   This means that large cache-cold executables start significantly faster.
> >   Launching X11+KDE+mozilla goes from 23 seconds to 16.  Starting OpenOffice
> >   seems to be 2x to 3x faster, and starting Konqueror maybe 3x faster too. 
> >   Interesting.
> > 
> >   This might cause weird thing to happen, especially on small-memory machines.
> 
> That's great. It would be nice to have this as a sysctl or perhaps
> some heuristic based on file size and available memory for 2.6.
> 

We shouldn't be putting this in-kernel, really.  Userspace can obtain
the same results by running madvise(MADV_WILLNEED) against the mapping
immediately after setting it up.  So a simple

	map = mmap(...);
+	if (getenv("MAP_PREFAULT"))
+		madvise(map, len, MADV_WILLNEED);

in glibc is enough.

That will work on 2.4, too.  I haven't tested that though.