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

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Message-ID: <CB1B361E45A85849902B25342E88900501CFDC311187@ABGEX70E.FSC.NET>
Date:	Wed, 11 Jan 2012 11:52:40 +0100
From:	"Borzenkov, Andrey" <andrey.borzenkov@...fujitsu.com>
To:	Eric Dumazet <eric.dumazet@...il.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)



> -----Original Message-----
> From: Eric Dumazet [mailto:eric.dumazet@...il.com]
> Sent: Wednesday, January 11, 2012 2:37 PM
> To: Borzenkov, Andrey
> Cc: 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 11:18 +0100, Borzenkov, Andrey a écrit :
> 
> > What can be the reason for system consuming half of physical memory for
> page tables?
> >
> 
> Why dont you use hugepages to map oracle SGA ?
> 

Colleagues responsible for Oracle are reconfiguring it now.

> 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

So page table for Oracle SGA 500G would be around 1G and shared by all Oracle clients. Is my assumption incorrect?