Re: O->A loan

[linbsd <jaimef%linbsd.org@localhost>]

On 12/26/11 18:53, YAMAMOTO Takashi wrote:
> 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
Hello Yamamoto-san
          I have run some benchmarks of build.sh -j16 on a 4-core HT 
amd64 box.
http://linbsd.org/yamt.txt


> > 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