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Message-ID: <50c22529-e0f4-9124-fdc0-c8da49300b18@linux.ibm.com>
Date:   Thu, 19 Jan 2023 10:59:02 -0500
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Subject: Re: [PATCH v4 4/7] s390/pci: Use dma-iommu layer
To:     Niklas Schnelle <schnelle@linux.ibm.com>,
        Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Wenjia Zhang <wenjia@linux.ibm.com>
Cc:     Gerd Bayer <gbayer@linux.ibm.com>,
        Pierre Morel <pmorel@linux.ibm.com>, iommu@lists.linux.dev,
        linux-s390@vger.kernel.org, borntraeger@linux.ibm.com,
        hca@linux.ibm.com, gor@linux.ibm.com,
        gerald.schaefer@linux.ibm.com, agordeev@linux.ibm.com,
        svens@linux.ibm.com, linux-kernel@vger.kernel.org,
        Julian Ruess <julianr@linux.ibm.com>
References: <20230104120543.308933-1-schnelle@linux.ibm.com>
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 <71b9e85d-960f-7403-0113-135746127f3b@linux.ibm.com>
 <a623049fb595480ffdf1130bbe800d79705cef03.camel@linux.ibm.com>
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From:   Matthew Rosato <mjrosato@linux.ibm.com>
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On 1/19/23 6:03 AM, Niklas Schnelle wrote:
>>>>>>>>>>>>>>>>>  
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>  static char *pci_sw_names[] = {
>>>>>>>>>>>>>>>>> - "Allocated pages",
>>>>>>>>>>>>>>>>> +/* TODO "Allocated pages", */
>>>>>>>>>
>>>>>>>>> ? Forgot to finish this?
> 
> Definitely forgot to remove the TODO. I think my latest plan was to
> just remove this counter. With the DMA API conversion the
> dma_map_ops.alloc and dma_map_ops.free move to common code and I don't
> see how we could differentiate these from map/unmap on our side. I'm
> not sure how helpful this counter really is either. If you're
> interested in how many pages are mapped long term I think it makes more
> sense to look at the difference between mapped and unmapped pages. What
> do you think?
>>>>>>>>

Sounds reasonable to me, but I also note that without this series, when viewing statistics for a device, mapped - unmapped != allocated.  Maybe allocated pages was already broken, or is it taking into account something else that mapped - unmapped would not (maybe mapping the same page multiple times)?