linux-kernel - Re: [PATCH] scsi: libcxgbi: use kvzalloc instead of opencoded kzalloc/vzalloc

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Message-ID: <c5a18804-3236-9688-2a3c-68184f0dd9e8@linux.com>
Date:   Sat, 1 Aug 2020 10:51:40 +0300
From:   Denis Efremov <efremov@...ux.com>
To:     Joe Perches <joe@...ches.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: libcxgbi: use kvzalloc instead of opencoded
 kzalloc/vzalloc



On 8/1/20 1:24 AM, Joe Perches wrote:
> On Sat, 2020-08-01 at 01:10 +0300, Denis Efremov wrote:
>>
>> On 8/1/20 12:58 AM, Joe Perches wrote:
>>> On Sat, 2020-08-01 at 00:55 +0300, Denis Efremov wrote:
>>>> Remove cxgbi_alloc_big_mem(), cxgbi_free_big_mem() functions
>>>> and use kvzalloc/kvfree instead.
>>>
>>> Sensible, thanks.
>>>
>>>> diff --git a/drivers/scsi/cxgbi/libcxgbi.c b/drivers/scsi/cxgbi/libcxgbi.c
>>> []
>>>> @@ -77,9 +77,9 @@ int cxgbi_device_portmap_create(struct cxgbi_device *cdev, unsigned int base,
>>>>  {
>>>>  	struct cxgbi_ports_map *pmap = &cdev->pmap;
>>>>  
>>>> -	pmap->port_csk = cxgbi_alloc_big_mem(max_conn *
>>>> -					     sizeof(struct cxgbi_sock *),
>>>> -					     GFP_KERNEL);
>>>> +	pmap->port_csk = kvzalloc(array_size(max_conn,
>>>> +					     sizeof(struct cxgbi_sock *)),
>>>> +				  GFP_KERNEL);
>>>
>>> missing __GFP_NOWARN
>>>
>>
>> kvmalloc_node adds __GFP_NOWARN internally to kmalloc call
>> https://elixir.bootlin.com/linux/v5.8-rc4/source/mm/util.c#L568
> 
> Only when there's a fallback, and the fallback does not.
> 

Sorry, Joe, I don't understand why do we need to add __GFP_NOWARN here.

We use GFP_KERNEL for allocation. cxgbi_alloc_big_mem adds __GFP_NOWARN only to kzalloc().
kvzalloc is: kvmalloc(size, flags | __GFP_ZERO)
kvmalloc is: kvmalloc_node(size, flags, NUMA_NO_NODE)
kvmalloc_node: 
	if ((flags & GFP_KERNEL) != GFP_KERNEL)           // false, flags == GFP_KERNEL|__GFP_ZERO
		return kmalloc_node(size, flags, node);

	if (size > PAGE_SIZE) {
		kmalloc_flags |= __GFP_NOWARN;            // add __GFP_NOWARN for "big" allocations

		if (!(kmalloc_flags & __GFP_RETRY_MAYFAIL))
			kmalloc_flags |= __GFP_NORETRY;
	}

	// kmalloc_flags == GFP_KERNEL|__GFP_ZERO|__GFP_NOWARN if size > PAGE_SIZE
	ret = kmalloc_node(size, kmalloc_flags, node);    

	if (ret || size <= PAGE_SIZE)
		return ret;

	// flags == GFP_KERNEL|__GFP_ZERO
	return __vmalloc_node(size, 1, flags, node,
			__builtin_return_address(0));

So, to my understanding the difference is only that cxgbi_alloc_big_mem adds __GFP_NOWARN
to kzalloc unconditionally, kvzalloc adds __GFP_NOWARN to kmalloc_node if size > PAGE_SIZE.
We use: max_conn * sizeof(struct cxgbi_sock *) in allocation. max_conn can be either
CXGBI_MAX_CONN or CXGB4I_MAX_CONN. CXGBI_MAX_CONN == 16384, CXGB4I_MAX_CONN == 16384.
Thus the allocation is bigger than PAGE_SIZE and kvmalloc_node adds __GFP_NOWARN to the
kmalloc_node call. Maybe I missed something?

Thanks,
Denis