Re: O->A loan

[yamt%mwd.biglobe.ne.jp@localhost (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