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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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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