linux-kernel - RE: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast (de)inflating & fast live migration

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Date:   Thu, 27 Oct 2016 00:51:13 +0000
From:   "Li, Liang Z" <liang.z.li@...el.com>
To:     "Hansen, Dave" <dave.hansen@...el.com>,
        "mst@...hat.com" <mst@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        "quintela@...hat.com" <quintela@...hat.com>,
        "dgilbert@...hat.com" <dgilbert@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "cornelia.huck@...ibm.com" <cornelia.huck@...ibm.com>,
        "amit.shah@...hat.com" <amit.shah@...hat.com>
Subject: RE: [RESEND PATCH v3 kernel 0/7] Extend virtio-balloon for fast
 (de)inflating & fast live migration

> On 10/26/2016 03:06 AM, Li, Liang Z wrote:
> > I am working on Dave's new bitmap schema, I have finished the part of
> > getting the 'hybrid scheme bitmap' and found the complexity was more
> > than I expected. The main issue is more memory is required to save the
> > 'hybrid scheme bitmap' beside that used to save the raw page bitmap,
> > for the worst case, the memory required is 3 times than that in the
> > previous implementation.
> 
> Really?  Could you please describe the scenario where this occurs?
> > I am wondering if I should continue, as an alternative solution, how
> > about using PFNs array when inflating/deflating only a few pages?
> > Things will be much more simple.
> 
> Yes, using pfn lists is more efficient than using bitmaps for sparse bitmaps.
> Yes, there will be cases where it is preferable to just use pfn lists vs. any kind
> of bitmap.
> 
> But, what does it matter?  At least with your current scheme where we go
> out and collect get_unused_pages(), we do the allocation up front.  The
> space efficiency doesn't matter at all for small sizes since we do the constant-
> size allocation *anyway*.
> 
> I'm also pretty sure you can pack the pfn and page order into a single 64-bit
> word and have no bitmap for a given record.  That would make it pack just as
> well as the old pfns alone.  Right?

Yes, thanks for reminding, I am using 128 bit now, I will change it to 64 bit.
Let me finish the v4 first.

Thanks!
Liang