linux-kernel - Re: [PATCH 4/4] RDMA/umem: batch page unpin in __ib_mem

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Date:   Fri, 5 Feb 2021 17:00:37 +0000
From:   Joao Martins <joao.m.martins@...cle.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        John Hubbard <jhubbard@...dia.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Doug Ledford <dledford@...hat.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH 4/4] RDMA/umem: batch page unpin in __ib_mem_release()



On 2/4/21 8:00 PM, Jason Gunthorpe wrote:
> On Wed, Feb 03, 2021 at 04:15:53PM -0800, John Hubbard wrote:
>>> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
>>> index 2dde99a9ba07..ea4ebb3261d9 100644
>>> +++ b/drivers/infiniband/core/umem.c
>>> @@ -47,17 +47,17 @@
>>>   static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int dirty)
>>>   {
>>> -	struct sg_page_iter sg_iter;
>>> -	struct page *page;
>>> +	bool make_dirty = umem->writable && dirty;
>>> +	struct scatterlist *sg;
>>> +	int i;
>>
>> Maybe unsigned int is better, so as to perfectly match the scatterlist.length.
> 
> Yes please
> 
Fixed in v2.

>>>   	if (umem->nmap > 0)
>>>   		ib_dma_unmap_sg(dev, umem->sg_head.sgl, umem->sg_nents,
>>>   				DMA_BIDIRECTIONAL);
>>> -	for_each_sg_page(umem->sg_head.sgl, &sg_iter, umem->sg_nents, 0) {
>>> -		page = sg_page_iter_page(&sg_iter);
>>> -		unpin_user_pages_dirty_lock(&page, 1, umem->writable && dirty);
>>> -	}
>>> +	for_each_sg(umem->sg_head.sgl, sg, umem->nmap, i)
>>
>> The change from umem->sg_nents to umem->nmap looks OK, although we should get
>> IB people to verify that there is not some odd bug or reason to leave it as is.
> 
> No, nmap wouldn't be right here. nmap is the number of dma mapped SGLs
> in the list and should only be used by things doing sg_dma* stuff.
> 
> umem->sg_nents is the number of CPU SGL entries and is the correct
> thing here.
> 

And this was fixed in v2 as well.