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

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Date:	Wed, 29 Aug 2007 15:36:40 -0700
From:	Dave Hansen <haveblue@...ibm.com>
To:	balbir@...ux.vnet.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

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. :)

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.

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.  

-- Dave

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