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

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Message-ID: <4F1445A6.4030503@redhat.com>
Date:	Mon, 16 Jan 2012 17:43:34 +0200
From:	Avi Kivity <avi@...hat.com>
To:	"Borzenkov, Andrey" <andrey.borzenkov@...fujitsu.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	"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)

On 01/13/2012 07:20 AM, Borzenkov, Andrey wrote:
> > > 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?
> > >
> > 
> > The second assumption is incorrect.  So fully populated the 2000
> > processes would consume 2T; they just haven't accessed all the SGA yet.
> > 
>
> Does kernel ever free allocated page tables, or once allocated they stick for the process lifetime? 

munmap() will free them, but that doesn't apply here.  Linux doesn't
swap page tables.

-- 
error compiling committee.c: too many arguments to function

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