Re: O->A loan

[yamt%mwd.biglobe.ne.jp@localhost (YAMAMOTO Takashi)]

hi,

> I did not remove DIAGNOSTIC.
> Would you like me to rerun without DIAGNOSTIC?

yes, please.

YAMAMOTO Takashi

> On Thu, 12 Jan 2012, YAMAMOTO Takashi wrote:
> 
>> Date: Thu, 12 Jan 2012 03:14:33 +0000 (UTC)
>> From: YAMAMOTO Takashi <yamt%mwd.biglobe.ne.jp@localhost>
>> To: jaimef%mauthesis.com@localhost
>> Cc: chuq%chuq.com@localhost, tech-kern%netbsd.org@localhost
>> Subject: Re: O->A loan
>> 
>> hi,
>>
>> thanks for benchmark!
>>
>> was it without DIAGNOSTIC?
>>
>> YAMAMOTO Takashi
>>
>>> Hello Yamamoto-san,
>>>
>>> I ran dbench on the same system with yamt-pagecache, yamt-pagecache
>>> without a-o loan, and yamt-pagecache-base3.
>>> http://linbsd.org/yamt.png
>>> The tests were run three times on each kernel and the results were
>>> consistent between reboots/runs.
>>>
>>> Thanks.
>>>
>>> On Tue, 27 Dec 2011, YAMAMOTO Takashi wrote:
>>>
>>>> Date: Tue, 27 Dec 2011 02:53:29 +0000 (UTC)
>>>> From: YAMAMOTO Takashi <yamt%mwd.biglobe.ne.jp@localhost>
>>>> To: chuq%chuq.com@localhost
>>>> Cc: tech-kern%netbsd.org@localhost
>>>> Subject: Re: O->A loan
>>>>
>>>> hi,
>>>>
>>>> i made read with O->A loaning work for easy cases (ie. no locking 
>>>> difficulty)
>>>> on yamt-pagecache branch so that someone interested can benchmark.
>>>>
>>>> YAMAMOTO Takashi
>>>>
>>>>> hi,
>>>>>
>>>>>> On Tue, Nov 29, 2011 at 06:38:27AM +0000, YAMAMOTO Takashi wrote:
>>>>>>> O->A loaned pages installed on the user address space would have a 
>>>>>>> different
>>>>>>> owner than the usual map->entry.uvm_obj.
>>>>>>> although it was not a problem when you wrote this patch, at least some
>>>>>>> non-mechanical changes would be required after the recent locking
>>>>>>> changes in this area.  namely, uvm_map_lock_entry etc now assumes that
>>>>>>> any pages mapped in a map entry belong to either the entry's amap or
>>>>>>> underlying object.
>>>>>>
>>>>>> ok, I didn't think it would be entirely mechanical.  :-)
>>>>>>
>>>>>> what if the O->A loan code also changed the entry's uvm_obj to be the 
>>>>>> vnode
>>>>>> that the pages really belong to?  if the loan range in the amap is fully
>>>>>> populated (which it is in this context) then that shouldn't affect the
>>>>>> logical contents of the entry, it would just cause anyone locking the 
>>>>>> entry
>>>>>> to also lock the vnode.  if the range of the loan is smaller than the
>>>>>> range of the entry, we could split the entry.  do you think that would 
>>>>>> work?
>>>>>
>>>>> it might work, but i have some concerns:
>>>>> - entry fragmentation
>>>>> - the extra uobj reference keeps the file even after unlink
>>>>>
>>>>> YAMAMOTO Takashi
>>>>>
>>>>>>
>>>>>> -Chuck