linux-kernel - Re: [PATCH v4 5/6] iova: Add iova_len argument to init_iova

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Message-ID: <099da8be-00dc-09cb-d72c-8e7b4b724f7c@huawei.com>
Date:   Mon, 2 Aug 2021 18:18:45 +0100
From:   John Garry <john.garry@...wei.com>
To:     Robin Murphy <robin.murphy@....com>, Will Deacon <will@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <sakari.ailus@...ux.intel.com>,
        <mst@...hat.com>, <airlied@...ux.ie>, <gregkh@...uxfoundation.org>,
        <linuxarm@...wei.com>, <jonathanh@...dia.com>,
        <iommu@...ts.linux-foundation.org>, <thierry.reding@...il.com>,
        <daniel@...ll.ch>, <bingbu.cao@...el.com>, <digetx@...il.com>,
        <mchehab@...nel.org>, <jasowang@...hat.com>,
        <tian.shu.qiu@...el.com>
Subject: Re: [PATCH v4 5/6] iova: Add iova_len argument to init_iova_domain()

On 02/08/2021 17:40, John Garry wrote:
> On 02/08/2021 17:16, Robin Murphy wrote:
>> On 2021-08-02 17:06, John Garry wrote:
>>> On 02/08/2021 16:06, Will Deacon wrote:
>>>> On Wed, Jul 14, 2021 at 06:36:42PM +0800, John Garry wrote:
>>>>> Add max opt argument to init_iova_domain(), and use it to set the 
>>>>> rcaches
>>>>> range.
>>>>>
>>>>> Also fix up all users to set this value (at 0, meaning use default).
>>>> Wrap that in init_iova_domain_defaults() to avoid the mysterious 0?
>>>
>>> Sure, I can do something like that. I actually did have separate 
>>> along those lines in v3 before I decided to change it.
>>
>> Y'know, at this point I'm now starting to seriously wonder whether 
>> moving the rcaches into iommu_dma_cookie wouldn't make a whole lot of 
>> things simpler... :/
> 
> As I see, the rcache stuff isn't really specific to IOVA anyway, so it 
> seems sane.
> 
>>
>> Does that sound like crazy talk to you, or an idea worth entertaining?
> 
> If you're going to start moving things, has anyone considered putting 
> rcache support in lib as a generic solution to "Magazines and Vmem: .." 
> paper?

Having said that, I still think that the rcache code has certain 
scalability issues, as discussed before. So making more generic and then 
discarding would be less than ideal.

Thanks,
john