Re: [PATCH v2] mm: add account_locked_vm utility function

[Daniel Jordan]

On Sat, May 25, 2019 at 02:51:18PM -0700, Andrew Morton wrote:
> On Fri, 24 May 2019 13:50:45 -0400 Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> wrote:
> 
> > locked_vm accounting is done roughly the same way in five places, so
> > unify them in a helper.  Standardize the debug prints, which vary
> > slightly, but include the helper's caller to disambiguate between
> > callsites.
> > 
> > Error codes stay the same, so user-visible behavior does too.  The one
> > exception is that the -EPERM case in tce_account_locked_vm is removed
> > because Alexey has never seen it triggered.
> > 
> > ...
> >
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -1564,6 +1564,25 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> >  int get_user_pages_fast(unsigned long start, int nr_pages,
> >  			unsigned int gup_flags, struct page **pages);
> >  
> > +int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc,
> > +			struct task_struct *task, bool bypass_rlim);
> > +
> > +static inline int account_locked_vm(struct mm_struct *mm, unsigned long pages,
> > +				    bool inc)
> > +{
> > +	int ret;
> > +
> > +	if (pages == 0 || !mm)
> > +		return 0;
> > +
> > +	down_write(&mm->mmap_sem);
> > +	ret = __account_locked_vm(mm, pages, inc, current,
> > +				  capable(CAP_IPC_LOCK));
> > +	up_write(&mm->mmap_sem);
> > +
> > +	return ret;
> > +}
> 
> That's quite a mouthful for an inlined function.  How about uninlining
> the whole thing and fiddling drivers/vfio/vfio_iommu_type1.c to suit. 
> I wonder why it does down_write_killable and whether it really needs
> to...

Sure, I can uninline it.  vfio changelogs don't show a particular reason for
_killable[1].  Maybe Alex has something to add.  Otherwise I'll respin without
it since the simplification seems worth removing _killable.

[1] 0cfef2b7410b ("vfio/type1: Remove locked page accounting workqueue")