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Date: Sat, 25 May 2019 14:51:18 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v2] mm: add account_locked_vm utility function
Message-Id: <20190525145118.bfda2d75a14db05a001e49ad@linux-foundation.org>
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	<20190524175045.26897-1-daniel.m.jordan@oracle.com>
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To: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>, Alan Tull <atull@kernel.org>, Alex Williamson <alex.williamson@redhat.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Christoph Lameter <cl@linux.com>, Christophe Leroy <christophe.leroy@c-s.fr>, Davidlohr Bueso <dave@stgolabs.net>, Jason Gunthorpe <jgg@mellanox.com>, Mark Rutland <mark.rutland@arm.com>, Michael Ellerman <mpe@ellerman.id.au>, Moritz Fischer <mdf@kernel.org>, Paul Mackerras <paulus@ozlabs.org>, Steve Sistare <steven.sistare@oracle.com>, Wu Hao <hao.wu@intel.com>, linux-mm@kvack.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-fpga@vger.kernel.org, linux-kernel@vger.kernel.org
List-ID: <linux-fpga@vger.kernel.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...