linux-kernel - Re: __vm_enough_memory(), OVERCOMMIT

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Message-ID: <20081022092736.2a0795d1@lxorguk.ukuu.org.uk>
Date:	Wed, 22 Oct 2008 09:27:36 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	hooanon05@...oo.co.jp
Cc:	linux-kernel@...r.kernel.org
Subject: Re: __vm_enough_memory(), OVERCOMMIT_NEVER, current->mm, kernel
 thread

> In your first option, write() to the exported tmpfs will produce the
> warning on nfs server even if much memory is left. I don't think it is a

No - the shmem routine would use vm_enough_memory_fs which wouldn't care
if current->mm is NULL, but the others would check.

> good idea.
> I'd suggest to make __vm_enough_memory() would skip the 3% adjustment
> only.
> 
> --- /src/linux-2.6/linux-2.6.27/mm/mmap.c	2008-10-10 07:13:53.000000000 +0900
> +++ /tmp/mmap.c	2008-10-22 08:07:09.000000000 +0900
> @@ -173,9 +173,10 @@
>  		allowed -= allowed / 32;
>  	allowed += total_swap_pages;
>  
> -	/* Don't let a single process grow too big:
> +	/* Don't let a single user process grow too big:
>  	   leave 3% of the size of this process for other processes */
> -	allowed -= mm->total_vm / 32;
> +	if (mm)
> +		allowed -= mm->total_vm / 32;

Doing this means we lose the ability to trap incorrect calls to
vm_enough_memory.

Alan
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