Re: O->A loan

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

hi,

> hi,
> 
>> On Sun, Nov 20, 2011 at 06:52:10PM +0000, YAMAMOTO Takashi wrote:
>>> hi,
>>> 
>>> i'd like to to either fix or remove O->A page loaning.
>>> 
>>> the biggest problem is the lack of users.  thus no way to test.
>>> any ideas?
>> 
>> some years ago I wrote some prototype code to use the O->A loaning for
>> read() and write().  the read() side worked, I don't think I had tested
>> the write() side so it probably has problems.  the patch is still around:
>> ftp://ftp.netbsd.org/pub/NetBSD/misc/chs/diff.uvm_readloan.8
>> 
>> it's quite a bit out of date, but I think most of the changes needed
>> to update it would be mechanical.
> 
> i'll take a look.  thanks.

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.

YAMAMOTO Takashi

> 
> did it (at least the read() side) have actual performance benefit
> compared to dumb copying?
> 
> YAMAMOTO Takashi
> 
>> 
>> -Chuck