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

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 24 May 2019 13:50:45 -0400 Daniel Jordan <daniel.m.jordan@oracle.com> 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...