[Gllug] HugePages

[Richard Jones]

On Thu, Oct 28, 2010 at 07:06:45PM +0100, James Courtier-Dutton wrote:
> My understanding of hugepages is that you only use them if you
> really have to.  The reason to have hugepages is that the x86/x64
> CPU has a fixed size page table. I.e. How many pages it can refer
> to.  If you have more physical memory than the CPU can reference
> with normal sized pages, one has to then use hugepages.

The above is a load of drivel from beginning to end.

Can't help with the original problem unfortunately.  It sounds very
specific to the machine and I'm afraid you need to investigate it from
first principles on that machine.  Luckily it sounds like you have a
good, reliable reproducer (ie. 'ls' and other commands taking a long
time to run).  Does the situation improve if you give reduce the
hugepage allocation by a smallish amount, say, 1 or 2 GB?

RHEL 6 and upstream have a wonderful feature called Transparent
Hugepages which makes all this business of statically allocating a
structure at boot time go away.  Here is Andrea's talk from the KVM
Forum:

http://www.linux-kvm.org/wiki/images/9/9e/2010-forum-thp.pdf

Rich.

-- 
Richard Jones
Red Hat
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