Re: [-mm PATCH] Memory controller improve user interface [message #19814] |
Wed, 29 August 2007 22:18 |
Dave Hansen
Messages: 240 Registered: October 2005
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Senior Member |
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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.
-- Dave
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Re: [-mm PATCH] Memory controller improve user interface [message #19816 is a reply to message #19814] |
Wed, 29 August 2007 22:20 |
Paul Menage
Messages: 642 Registered: September 2006
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Senior Member |
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On 8/29/07, Dave Hansen <haveblue@us.ibm.com> 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.
I'd argue that having the user's specified limit be truncated to the
page size is less confusing than giving an EINVAL if it's not page
aligned.
Paul
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Re: [-mm PATCH] Memory controller improve user interface [message #19833 is a reply to message #19814] |
Wed, 29 August 2007 22:27 |
Balbir Singh
Messages: 491 Registered: August 2006
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Senior Member |
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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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Re: [-mm PATCH] Memory controller improve user interface [message #19851 is a reply to message #19850] |
Thu, 30 August 2007 09:13 |
Balbir Singh
Messages: 491 Registered: August 2006
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Senior Member |
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KAMEZAWA Hiroyuki wrote:
> On Thu, 30 Aug 2007 04:07:11 +0530
> Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
>> 1. Several people recommended it
>> 2. Herbert mentioned that they've moved to that interface and it
>> was working fine for them.
>>
>
> I have no strong opinion. But how about Mega bytes ? (too big ?)
> There will be no rounding up/down problem.
>
Here is what I am thinking, allow the user to input bytes/kilobytes/
megabytes or gigabytes. Store the data internally in kilobytes or
PFN. I prefer kilobytes (no rounding issues), but while implementing
limits we round up to the closest PFN.
--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
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