linux-kernel - Re: A question about using a private anonymous mmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20090605120618.0c074050.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 5 Jun 2009 12:06:18 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Julian Phillips <julian@...ntumfyre.co.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: A question about using a private anonymous mmap

On Thu, 4 Jun 2009 17:48:29 +0100 (BST)
Julian Phillips <julian@...ntumfyre.co.uk> wrote:

> I have a program which creates a reasonably large private anonymous map. 
> The program then writes into a few places in the map, but ends up reading 
> from all of them.
> 
> When I run this program on a system running 2.6.20.7 the process only ever 
> seems to use enough memory to hold the data that has actually been written 
> (well - in units of PAGE_SIZE).  When I run the program on a system 
> running 2.6.24.5 then as it reads the map the amount of memory used 
> continues to increase until the complete map has actually been allocated 
> (and since the total size is greater than the physically available RAM 
> causes swapping).  Basically I seem to be seeing copy-on-read instead of 
> copy-on-write type behaviour.
> 
> Is this an expected change, and is there any option I can tweak to get the 
> old behaviour back?
> 

It comes from removal of ZERO_PAGE.

IMHO, What you can do is mmap(/dev/zero, MAP_PRIVATE) instead of ANON.

Thanks,
-Kame

> TIA,
> 
> -- 
> Julian
> 
>   ---
> I can't die until the government finds a safe place to bury my liver.
>  		-- Phil Harris
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/