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Date:   Tue, 12 Mar 2019 15:15:22 +0800
From:   Jason Wang <>
To:     "Michael S. Tsirkin" <>
Cc:     Andrea Arcangeli <>,,,,,,, Jerome Glisse <>
Subject: Re: [RFC PATCH V2 5/5] vhost: access vq metadata through kernel
 virtual address

On 2019/3/12 上午11:50, Michael S. Tsirkin wrote:
>>>> Using direct mapping (I
>>>> guess kernel will always try hugepage for that?) should be better and we can
>>>> even use it for the data transfer not only for the metadata.
>>>> Thanks
>>> We can't really. The big issue is get user pages. Doing that on data
>>> path will be slower than copyXuser.
>> I meant if we can find a way to avoid doing gup in datapath. E.g vhost
>> maintain a range tree and add or remove ranges through MMU notifier. Then in
>> datapath, if we find the range, then use direct mapping otherwise
>> copy_to_user().
>> Thanks
> We can try. But I'm not sure there's any reason to think there's any
> locality there.

Ok, but what kind of locality do you mean here?


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