linux-kernel - Re: [PATCH 1/6] iommu: Move IOVA power-of-2 roundup into allocator

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Message-ID: <08c0f4b9-8713-fa97-3986-3cfb0d6b820b@huawei.com>
Date:   Mon, 22 Mar 2021 15:01:00 +0000
From:   John Garry <john.garry@...wei.com>
To:     Robin Murphy <robin.murphy@....com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "hch@....de" <hch@....de>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>
CC:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>
Subject: Re: [PATCH 1/6] iommu: Move IOVA power-of-2 roundup into allocator

On 19/03/2021 19:20, Robin Murphy wrote:

Hi Robin,

>> So then we have the issue of how to dynamically increase this rcache
>> threshold. The problem is that we may have many devices associated with
>> the same domain. So, in theory, we can't assume that when we increase
>> the threshold that some other device will try to fast free an IOVA which
>> was allocated prior to the increase and was not rounded up.
>>
>> I'm very open to better (or less bad) suggestions on how to do this ...
> ...but yes, regardless of exactly where it happens, rounding up or not
> is the problem for rcaches in general. I've said several times that my
> preferred approach is to not change it that dynamically at all, but
> instead treat it more like we treat the default domain type.
> 

Can you remind me of that idea? I don't remember you mentioning using 
default domain handling as a reference in any context.

Thanks,
John