Re: [LSF/MM] schedule suggestion

[Jerome Glisse <jglisse@redhat.com>]

On Thu, Apr 19, 2018 at 02:31:07PM -0400, Jeff Layton wrote:
> On Thu, 2018-04-19 at 13:26 -0400, Jerome Glisse wrote:
> > On Thu, Apr 19, 2018 at 12:58:39PM -0400, Jeff Layton wrote:
> > > On Thu, 2018-04-19 at 12:30 -0400, Jerome Glisse wrote:
> > > > On Thu, Apr 19, 2018 at 07:43:56AM -0700, Matthew Wilcox wrote:
> > > > > On Thu, Apr 19, 2018 at 10:38:25AM -0400, Jerome Glisse wrote:
> > > > > > Oh can i get one more small slot for fs ? I want to ask if they are
> > > > > > any people against having a callback everytime a struct file is added
> > > > > > to a task_struct and also having a secondary array so that special
> > > > > > file like device file can store something opaque per task_struct per
> > > > > > struct file.
> > > > > 
> > > > > Do you really want something per _thread_, and not per _mm_?
> > > > 
> > > > Well per mm would be fine but i do not see how to make that happen with
> > > > reasonable structure. So issue is that you can have multiple task with
> > > > same mm but different file descriptors (or am i wrong here ?) thus there
> > > > would be no easy way given a struct file to lookup the per mm struct.
> > > > 
> > > > So as a not perfect solution i see a new array in filedes which would
> > > > allow device driver to store a pointer to their per mm data structure.
> > > > To be fair usualy you will only have a single fd in a single task for
> > > > a given device.
> > > > 
> > > > If you see an easy way to get a per mm per inode pointer store somewhere
> > > > with easy lookup i am all ears :)
> > > > 
> > > 
> > > I may be misunderstanding, but to be clear: struct files don't get
> > > added to a thread, per-se.
> > > 
> > > When userland calls open() or similar, the struct file gets added to
> > > the files_struct. Those are generally shared with other threads within
> > > the same process. The files_struct can also be shared with other
> > > processes if you clone() with the right flags.
> > > 
> > > Doing something per-thread on every open may be rather difficult to do.
> > 
> > Basicly i want a callback in __fd_install(), do_dup2(), dup_fd() and
> > add void * *private_data; to struct fdtable (also a default array to
> > struct files_struct). The callback would be part of struct file_operations.
> > and only call if it exist (os overhead is only for device driver that
> > care).
> > 
> > Did i miss something fundamental ? copy_files() call dup_fd() so i
> > should be all set here.
> > 
> > I will work on patches i was hoping this would not be too much work.
> > 
> 
> No, I think I misunderstood. I was thinking you wanted to iterate over
> all of the threads that might be associated with a struct file, and
> that's rather non-trivial.
> 
> A callback when you add a file to the files_struct seems like it would
> probably be OK (in principle).

Well scratch that whole idea, i would need to add a new array to task
struct which make it a lot less appealing. Hence a better solution is
to instead have this as part of mm (well indirectly).

Thanks folks for chimming in. I will discuss this in my mmu_notifier
session.

Cheers,
J�r�me