linux-kernel - Re: [PATCH v11 01/12] iova: Export alloc_iova_fast() and free_iova

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Message-ID: <d7b5967f-0a43-785a-82b0-74cce5993ba0@huawei.com>
Date:   Fri, 27 Aug 2021 10:03:03 +0100
From:   John Garry <john.garry@...wei.com>
To:     Yongji Xie <xieyongji@...edance.com>
CC:     Will Deacon <will@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>, kvm <kvm@...r.kernel.org>,
        Jason Wang <jasowang@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        Christian Brauner <christian.brauner@...onical.com>,
        Jonathan Corbet <corbet@....net>,
        "Matthew Wilcox" <willy@...radead.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Dan Carpenter" <dan.carpenter@...cle.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Liu Xiaodong <xiaodong.liu@...el.com>,
        <linux-fsdevel@...r.kernel.org>, Al Viro <viro@...iv.linux.org.uk>,
        "Stefan Hajnoczi" <stefanha@...hat.com>,
        <songmuchun@...edance.com>, Jens Axboe <axboe@...nel.dk>,
        He Zhe <zhe.he@...driver.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        <iommu@...ts.linux-foundation.org>, <bcrl@...ck.org>,
        <netdev@...r.kernel.org>, Joe Perches <joe@...ches.com>,
        Robin Murphy <robin.murphy@....com>,
        Mika Penttilä <mika.penttila@...tfour.com>
Subject: Re: [PATCH v11 01/12] iova: Export alloc_iova_fast() and
 free_iova_fast()

On 25/08/2021 13:17, Yongji Xie wrote:
>> JFYI, There was a preliminary discussion to move the iova rcache code
>> (which the iova fast alloc and free functions are based on) out of the
>> iova code and maybe into dma-iommu (being the only user). There was
>> other motivation.
>>
> Would it be better to move the code into ./lib as a general library?

For a start we/I think that the rcache could be removed from the IOVA 
code, but prob should stay in drivers/iommu. I had another IOVA issue to 
solve, which complicates things. No solid plans. Need to talk to Robin more.

> 
>> https://lore.kernel.org/linux-iommu/83de3911-145d-77c8-17c1-981e4ff825d3@arm.com/
>>
>> Having more users complicates that...
>>
> Do we have some plan for this work? From our test [1],
> iova_alloc_fast() is much better than iova_alloc(). So I'd like to use
> it as much as possible
> 
> [1]https://lore.kernel.org/kvm/CACycT3steXFeg7NRbWpo2J59dpYcumzcvM2zcPJAVe40-EvvEg@mail.gmail.com/

Well if you're alloc'ing and free'ing IOVAs a lot then I can imagine it is.

Thanks,
John