Re: [PATCH RFC 8/9] RDMA/umem: batch page unpin in __ib_mem_release()

[Joao Martins <joao.m.martins@oracle.com>]

On 12/9/20 10:59 AM, Joao Martins wrote:
> On 12/8/20 7:29 PM, Jason Gunthorpe wrote:
>> On Tue, Dec 08, 2020 at 05:29:00PM +0000, Joao Martins wrote:
>>
>>>  static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int dirty)
>>>  {
>>> +	bool make_dirty = umem->writable && dirty;
>>> +	struct page **page_list = NULL;
>>>  	struct sg_page_iter sg_iter;
>>> +	unsigned long nr = 0;
>>>  	struct page *page;
>>>  
>>> +	page_list = (struct page **) __get_free_page(GFP_KERNEL);
>>
>> Gah, no, don't do it like this!
>>
>> Instead something like:
>>
>> 	for_each_sg(umem->sg_head.sgl, sg, umem->nmap, i)
>> 	      unpin_use_pages_range_dirty_lock(sg_page(sg), sg->length/PAGE_SIZE,
>>                                                umem->writable && dirty);
>>
>> And have the mm implementation split the contiguous range of pages into
>> pairs of (compound head, ntails) with a bit of maths.
>>
> Got it :)
> 
> I was trying to avoid another exported symbol.
> 
> Albeit upon your suggestion below, it doesn't justify the efficiency/clearness lost.
> 
This more efficient suggestion of yours leads to a further speed up from:

	1073 rounds in 5.004 sec: 4663.622 usec / round (hugetlbfs)

to

	1370 rounds in 5.003 sec: 3651.562 usec / round (hugetlbfs)

Right after I come back from holidays I will follow up with this series in separate.

	Joao
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