linux-kernel - Re: [PATCH v20 4/7] virtio-balloon: VIRTIO_BALLOON_F

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Date:   Wed, 03 Jan 2018 17:00:28 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        willy@...radead.org
CC:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, mst@...hat.com,
        mhocko@...nel.org, akpm@...ux-foundation.org,
        mawilcox@...rosoft.com, david@...hat.com, cornelia.huck@...ibm.com,
        mgorman@...hsingularity.net, aarcange@...hat.com,
        amit.shah@...hat.com, pbonzini@...hat.com,
        liliang.opensource@...il.com, yang.zhang.wz@...il.com,
        quan.xu0@...il.com, nilal@...hat.com, riel@...hat.com
Subject: Re: [PATCH v20 4/7] virtio-balloon: VIRTIO_BALLOON_F_SG

On 01/03/2018 10:29 AM, Tetsuo Handa wrote:
> Matthew Wilcox wrote:
>> The radix tree convention is objectively awful, which is why I'm working
>> to change it.  Specifying the GFP flags at radix tree initialisation time
>> rather than allocation time leads to all kinds of confusion.  The preload
>> API is a pretty awful workaround, and it will go away once the XArray
>> is working correctly.  That said, there's no alternative to it without
>> making XBitmap depend on XArray, and I don't want to hold you up there.
>> So there's an xb_preload for the moment.
> I'm ready to propose cvbmp shown below as an alternative to xbitmap (but
> specialized for virtio-balloon case). Wei, can you do some benchmarking
> between xbitmap and cvbmp?
> ----------------------------------------
> cvbmp: clustered values bitmap

I don't think we need to replace xbitmap, at least at this stage. The 
new implementation doesn't look simpler at all, and virtio-balloon has 
worked well with xbitmap.

I would suggest you to send out the new implementation for discussion 
after this series ends, and justify with better performance results if 
you could get.

Best,
Wei