On Mon, Aug 24, 2009 at 11:51:07PM +0200, Toon Moene wrote:
> [ I found this e-mail address while surfing http://linux-mm.org -
> hope it's relevant. ]
>
> Is it possible to boot the Linux kernel in such a way as to *only*
> enable "huge" pages ?
>
> I ask this because my use of "da machine" is mostly running large
> Fortran programs, who need all memory of it anyway, so there's little to
> gain from small page sizes.
The kernel portion of the address space is already backed by huge PTEs so
you can ignore that. If you have a smaller number of fortran applications
that are consuming all of memory, then recompile them to use hugepages as
described in the HOWTO. Use hugeadm to get the system to dynamically allocate
hugepages where they are available with;
hugeadm --pool-pages-max 2M:$((TOTAL_MEMORY_IN_MEGABYTES/2))
and make them available with improved fragmentation control with
hugeadm --create-global-mounts
hugeadm --set-recommended-min_free_Kbytes
and then run your applications
hugectl --text --data --heap ./target_application
and it'll use hugepages when and where possible. You can do basic
monitoring with
grep Huge /proc/meminfo
You can also use /proc/PID/smaps to get a better view of which
portions of your application are really using hugepages by looking at
the KernelPageSize: and MMUPageSize: of each address range in use by
your application.
Caveats
o existance of hugeadm depends on your version of libhugetlbfs
o --set-recommended-min_free_kbytes is not in a release version
yet, just in the source repository
o smaps reporting the pagesize in use depends on your kernel
version and it's relatively recent
>
> [ Yes, I know this will make the occasional 'ls', 'rm' and 'mv' also at
> least 2 MB in size ]
>
It's not really possible because there are ABI assumptions about 4K that
would make loading normal binaries harder. On some architecture like PPC64,
it's less of a problem as binaries are aligned to 64K so those page sizes
can be used at least but on x86, a recompile is needed.
> Thanks in advance for any insight provided ... and happy hacking !
>
Hope this helped.
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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