linux-kernel - Re: [NEW]: Introducing shrink_all

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Date:	Sun, 15 Apr 2012 04:47:09 -0700 (PDT)
From:	PINTU KUMAR <pintu_agarwal@...oo.com>
To:	richard -rw- weinberger <richard.weinberger@...il.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"pintu.k@...sung.com" <pintu.k@...sung.com>
Subject: Re: [NEW]: Introducing shrink_all_memory from user space



> 
> This is fundamentally flawed.
> You're assuming that only one program will use this interface.
> Linux is a multi/user-tasking system

Dear Richard, Thank you for your comments.
I am sorry but this is meant only for *root* user.
That is only root user can do this: "echo 512 > /dev/shrinkmem"
If other user try to write in it: it says permission denied as follows:
pintu@...tu-ubuntu:~$ echo 512 > /dev/shrinkmem
-bash: /dev/shrinkmem: Permission denied

Moreover, this is mainly meant for mobile phones where there is only *one* user.

> 
> If we expose it to user space *every* program/user will try too free
> memory such that it
> can use more.
> Can you see the problem?
> 
As indicated above, every program/user cannot use it, as it requires root privileges.
Ok, you mean to say, every driver can call "shrink_all_memory" simultaneously??
Well, we can implement locking for that.
Anyways, I wrote a simple script to do this (echo 512 > /dev/shrinkmem) in a loop for 20 times from 2 different terminal (as root) and it works.
I cannot see any problem.
Can you elaborate more please?


Thanks,
Pintu
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