Re: [PATCH 07/25] mm/csky: Use mm_fault_accounting()

[Peter Xu]

On Wed, Jun 17, 2020 at 10:53:23AM -0700, Linus Torvalds wrote:
> On Wed, Jun 17, 2020 at 8:49 AM Peter Xu <peterx@xxxxxxxxxx> wrote:
> >
> > I don't think it's a must, but mmap_sem should not be required at least by
> > observing current code.  E.g., do_user_addr_fault() of x86 does the accounting
> > without mmap_sem even before this series.
> 
> All the accounting should be per-thread and not need any locking.
> 
> Which is why a remote GUP should never account to the remote mm - not
> only isn't there an unambiguous thread to account to (an mm can share
> many threads), but it would require locking not just for the remote
> update, but for all normal page faults.

But currently remote GUP will still do the page fault accounting on the remote
task_struct, am I right?  E.g., when the get_user_pages_remote() is called with
"tsk != current", it seems the faultin_page() will still do maj_flt/min_flt
accounting for that remote task/thread?

Thanks,

-- 
Peter Xu