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From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: akpm@linux-foundation.org, 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
Subject: Re: [PATCH] mm: add account_locked_vm utility function
Date: Fri, 24 May 2019 16:43:10 +1000	[thread overview]
Message-ID: <de375582-2c35-8e8a-4737-c816052a8e58@ozlabs.ru> (raw)
In-Reply-To: <20190520153020.mzvjsjwefwxz6cau@ca-dmjordan1.us.oracle.com>



On 21/05/2019 01:30, Daniel Jordan wrote:
> On Mon, May 20, 2019 at 04:19:34PM +1000, Alexey Kardashevskiy wrote:
>> On 04/05/2019 06:16, Daniel Jordan 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.
>>
>> And I rather liked that prints were different and tell precisely which
>> one of three each printk is.
> 
> I'm not following.  One of three...callsites?  But there were five callsites.


Well, 3 of them are mine, I was referring to them :)


> Anyway, I added a _RET_IP_ to the debug print so you can differentiate.


I did not know that existed, cool!


> 
>> I commented below but in general this seems working.
>>
>> Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> 
> Thanks!  And for the review as well.
> 
>>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>>> index 6b64e45a5269..d39a1b830d82 100644
>>> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
>>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>>> @@ -34,49 +35,13 @@
>>>  static void tce_iommu_detach_group(void *iommu_data,
>>>  		struct iommu_group *iommu_group);
>>>  
>>> -static long try_increment_locked_vm(struct mm_struct *mm, long npages)
>>> +static int tce_account_locked_vm(struct mm_struct *mm, unsigned long npages,
>>> +				 bool inc)
>>>  {
>>> -	long ret = 0, locked, lock_limit;
>>> -
>>>  	if (WARN_ON_ONCE(!mm))
>>>  		return -EPERM;
>>
>>
>> If this WARN_ON is the only reason for having tce_account_locked_vm()
>> instead of calling account_locked_vm() directly, you can then ditch the
>> check as I have never ever seen this triggered.
> 
> Great, will do.
> 
>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>>> index d0f731c9920a..15ac76171ccd 100644
>>> --- a/drivers/vfio/vfio_iommu_type1.c
>>> +++ b/drivers/vfio/vfio_iommu_type1.c
>>> @@ -273,25 +273,14 @@ static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
>>>  		return -ESRCH; /* process exited */
>>>  
>>>  	ret = down_write_killable(&mm->mmap_sem);
>>> -	if (!ret) {
>>> -		if (npage > 0) {
>>> -			if (!dma->lock_cap) {
>>> -				unsigned long limit;
>>> -
>>> -				limit = task_rlimit(dma->task,
>>> -						RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>>> -
>>> -				if (mm->locked_vm + npage > limit)
>>> -					ret = -ENOMEM;
>>> -			}
>>> -		}
>>> +	if (ret)
>>> +		goto out;
>>
>>
>> A single "goto" to jump just 3 lines below seems unnecessary.
> 
> No strong preference here, I'll take out the goto.
> 
>>> +int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc,
>>> +			struct task_struct *task, bool bypass_rlim)
>>> +{
>>> +	unsigned long locked_vm, limit;
>>> +	int ret = 0;
>>> +
>>> +	locked_vm = mm->locked_vm;
>>> +	if (inc) {
>>> +		if (!bypass_rlim) {
>>> +			limit = task_rlimit(task, RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>>> +			if (locked_vm + pages > limit) {
>>> +				ret = -ENOMEM;
>>> +				goto out;
>>> +			}
>>> +		}
>>
>> Nit:
>>
>> if (!ret)
>>
>> and then you don't need "goto out".
> 
> Ok, sure.
> 
>>> +		mm->locked_vm = locked_vm + pages;
>>> +	} else {
>>> +		WARN_ON_ONCE(pages > locked_vm);
>>> +		mm->locked_vm = locked_vm - pages;
>>
>>
>> Can go negative here. Not a huge deal but inaccurate imo.
> 
> I hear you, but setting a negative value to zero, as we had done previously,
> doesn't make much sense to me.


Ok then. I have not seen these WARN_ON for a very long time anyway.


-- 
Alexey

  reply	other threads:[~2019-05-24  6:43 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-03 20:16 Daniel Jordan
2019-05-03 23:28 ` Jason Gunthorpe
2019-05-07  3:09   ` Daniel Jordan
2019-05-20  6:19 ` Alexey Kardashevskiy
2019-05-20 15:30   ` Daniel Jordan
2019-05-24  6:43     ` Alexey Kardashevskiy [this message]
2019-05-24 17:50       ` [PATCH v2] " Daniel Jordan
2019-05-25 21:51         ` Andrew Morton
2019-05-28 15:04           ` Daniel Jordan
2019-05-29 18:56             ` Alex Williamson
2019-05-29 20:50               ` [PATCH v3] " Daniel Jordan
2019-06-03 19:15                 ` Alex Williamson
2019-05-29 18:05         ` [PATCH v2] " Ira Weiny
2019-05-29 18:35           ` Daniel Jordan

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