netdev - Re: [PATCH v10 01/17] iova: Export alloc_iova_fast() and free_iova

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Date:   Thu, 5 Aug 2021 21:31:43 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Yongji Xie <xieyongji@...edance.com>,
        Robin Murphy <robin.murphy@....com>
Cc:     kvm <kvm@...r.kernel.org>, "Michael S. Tsirkin" <mst@...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>,
        Joe Perches <joe@...ches.com>,
        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, linux-fsdevel@...r.kernel.org,
        Mika Penttilä <mika.penttila@...tfour.com>
Subject: Re: [PATCH v10 01/17] iova: Export alloc_iova_fast() and
 free_iova_fast()


在 2021/8/5 下午8:34, Yongji Xie 写道:
>> My main point, though, is that if you've already got something else
>> keeping track of the actual addresses, then the way you're using an
>> iova_domain appears to be something you could do with a trivial bitmap
>> allocator. That's why I don't buy the efficiency argument. The main
>> design points of the IOVA allocator are to manage large address spaces
>> while trying to maximise spatial locality to minimise the underlying
>> pagetable usage, and allocating with a flexible limit to support
>> multiple devices with different addressing capabilities in the same
>> address space. If none of those aspects are relevant to the use-case -
>> which AFAICS appears to be true here - then as a general-purpose
>> resource allocator it's rubbish and has an unreasonably massive memory
>> overhead and there are many, many better choices.
>>
> OK, I get your point. Actually we used the genpool allocator in the
> early version. Maybe we can fall back to using it.


I think maybe you can share some perf numbers to see how much 
alloc_iova_fast() can help.

Thanks


>