Re: hole-punch vs fault

[Matthew Wilcox <matthew@wil.cx>]

On Mon, Dec 02, 2013 at 09:33:18AM +0100, Jan Kara wrote:
> > Indeed, XIP could make use of the structures we already
> > have in the struct inode/address space to behave more like a normal
> > filesystem. We already use the mapping tree to store
> > per-page information that is used to serialise truncate vs page
> > faults, so why not make XIP do exactly the same thing? 
>   I believe that grabbing mmap_sem for writing during truncate (in case of
> ext2 around xip_truncate_page() & truncate_setsize() calls should do the
> trick. But I need to verify with lockdep that it doesn't introduce new
> locking problems.

Umm ... mmap_sem for write?  On each of the tasks that have a file mmaped?
I know we have double_down that orders by memory address, but I don't
think we have an N_down_write().

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."