linux-kernel - Re: [-mm PATCH] Memory controller improve user interface

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Message-ID: <46D5F6BF.2080607@linux.vnet.ibm.com>
Date:	Thu, 30 Aug 2007 04:14:15 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Dave Hansen <haveblue@...ibm.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux MM Mailing List <linux-mm@...ck.org>,
	David Rientjes <rientjes@...gle.com>,
	Linux Containers <containers@...ts.osdl.org>,
	Paul Menage <menage@...gle.com>
Subject: Re: [-mm PATCH]  Memory controller improve user interface

Dave Hansen wrote:
> On Thu, 2007-08-30 at 03:57 +0530, Balbir Singh wrote:
>> True, mmap() is a good example of such an interface for developers, I
>> am not sure about system admins though.
>>
>> To quote Andrew
>> <quote>
>> Reporting tools could run getpagesize() and do the arithmetic, but we
>> generally try to avoid exposing PAGE_SIZE, HZ, etc to userspace in this
>> manner.
>> </quote>
> 
> Well, rounding to PAGE_SIZE exposes PAGE_SIZE as well, just in a
> non-intuitive fashion. :)
> 

Agreed, but the user might choose to ignore it altogether.

> If we're going to modify what the user specifies, we should probably at
> least mandate that writes are only a "suggestion" and users must read
> back the value to ensure what actually got committed.
> 

Agreed, excellent suggestion!

> If we're going to round in any direction, shouldn't we round up?  If a
> user specifies 4097 bytes and uses two pages, we don't want to complain
> when they hit that second page.  
> 

Absolutely, I used rounding to mean round up, truncation for rounding down.

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