linux-kernel - RE: Extermeley large PageTables over 500G on kernel 2.6.32.49 (SLES11 SP1)

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Date:	Wed, 11 Jan 2012 12:19:40 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Borzenkov, Andrey" <andrey.borzenkov@...fujitsu.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: Extermeley large PageTables over 500G on kernel 2.6.32.49
 (SLES11 SP1)

Le mercredi 11 janvier 2012 à 11:52 +0100, Borzenkov, Andrey a écrit :

> Colleagues responsible for Oracle are reconfiguring it now.
> 

OK. Since your hardware supports 1GB hugepages, you might try to use
them as well. Not sure if your kernel is recent enough...

cat /proc/cmdline 
ro root=LABEL=/ hugepagesz=1GB hugepages=512 

> > If not, its normal to eat so much memory for page tables
> > 
> > grep VmPTE /proc/*/status
> > 
> > 
> 
> Forgive my ignorance. I thought that
> 
> 1. PTE is 8 bytes per page, which is 4K which gives 2K per 1M of memory
> 2. All processes sharing the same shared memory share the same page table

It depends how oracle maps its SGA.

It probably uses a method disallowing page table sharing.

Anyway, hugetables for this kind of workload is a must.



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