linux-kernel - Re: [RFC][2/3] Account and control virtual address space allocations

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Message-ID: <47E002CB.4090900@linux.vnet.ibm.com>
Date:	Tue, 18 Mar 2008 23:28:35 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Dave Hansen <haveblue@...ibm.com>
CC:	linux-mm@...ck.org, Hugh Dickins <hugh@...itas.com>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	David Rientjes <rientjes@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [RFC][2/3] Account and control virtual address space allocations

Dave Hansen wrote:
> On Tue, 2008-03-18 at 06:44 +0530, Balbir Singh wrote: 
>>> If you're going to do this, I think you need a couple of phases.  
>>>
>>> 1. update the vm_(un)acct_memory() functions to take an mm
>> There are other problems
>>
>> 1. vm_(un)acct_memory is conditionally dependent on VM_ACCOUNT. Look at
>> shmem_(un)acct_size for example
> 
> Yeah, but if VM_ACCOUNT isn't set, do you really want the controller
> accounting for them?  It's there for a reason. :)
> 

We are trying to account for virtual memory usage. Please see
http://lwn.net/Articles/5016/ to see what VM_ACCOUNT does or
Documentation/vm/overcommit-accounting. We want to account and control virtual
memory usage and not necessarily implement overcommit accounting

> The shmem_acct_size() helpers look good.  I wonder if we should be using
> that kind of things more generically.
> 

Yes, it is well written. I wish there were more such abstractions, but it does
not help us.

>> 2. These routines are not called from all contexts that we care about (look at
>> insert_special_mapping())
> 
> Could you explain why "we" care about it and why it isn't accounted for
> now?

It is accounted for in total_vm and that's why we care about :)

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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