Subject: Re: [PATCH 4/5] iommu: Separate IOVA rcache memories from iova_domain
 structure
To:     Robin Murphy <robin.murphy@arm.com>, <joro@8bytes.org>,
        <will@kernel.org>, <mst@redhat.com>, <jasowang@redhat.com>
CC:     <xieyongji@bytedance.com>, <linux-kernel@vger.kernel.org>,
        <iommu@lists.linux-foundation.org>,
        <virtualization@lists.linux-foundation.org>, <linuxarm@huawei.com>,
        <thunder.leizhen@huawei.com>, <baolu.lu@linux.intel.com>
References: <1632477717-5254-1-git-send-email-john.garry@huawei.com>
 <1632477717-5254-5-git-send-email-john.garry@huawei.com>
 <2c58036f-d9aa-61f9-ae4b-f6938a135de5@huawei.com>
 <85c60ef4-e1af-c947-a2ed-b63c4fef36c3@arm.com>
From:   John Garry <john.garry@huawei.com>
Message-ID: <045030ed-0151-6259-e336-4235d6456223@huawei.com>
Date:   Wed, 22 Dec 2021 11:53:11 +0000
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On 20/12/2021 13:57, Robin Murphy wrote:
>> Do you have any thoughts on this patch? The decision is whether we 
>> stick with a single iova domain structure or support this super 
>> structure for iova domains which support the rcache. I did not try the 
>> former - it would be do-able but I am not sure on how it would look.
> 
> TBH I feel inclined to take the simpler approach of just splitting the 
> rcache array to a separate allocation, making init_iova_rcaches() public 
> (with a proper return value), and tweaking put_iova_domain() to make 
> rcache cleanup conditional. A residual overhead of 3 extra pointers in 
> iova_domain doesn't seem like *too* much for non-DMA-API users to bear. 

OK, fine. So I tried as you suggested and it looks ok to me.

I'll send something out at rc1.

> Unless you want to try generalising the rcache mechanism completely away 
> from IOVA API specifics, it doesn't seem like there's really enough to 
> justify the bother of having its own distinct abstraction layer.

Yeah, I don't see that as necessary.

However something which could be useful is to separate the magazine code 
out for other possible users.

Thanks!
John