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

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Message-ID: <46D5F2BB.8010203@linux.vnet.ibm.com>
Date:	Thu, 30 Aug 2007 03:57:07 +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 03:34 +0530, Balbir Singh wrote:
>> I've thought about this before. The problem is that a user could
>> set his limit to 10000 bytes, but would then see the usage and
>> limit round to the closest page boundary. This can be confusing
>> to a user. 
> 
> True, but we're lying if we allow a user to set their limit there,
> because we can't actually enforce a limit at 8,192 bytes vs 10,000.
> They're the same limit as far as the kernel is concerned.
> 
> Why not just -EINVAL if the value isn't page-aligned?  There are plenty
> of interfaces in the kernel that require userspace to know the page
> size, so this shouldn't be too difficult.

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>

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