linux-kernel - RE: [PATCH RFC kernel] balloon: speed up inflating/deflating process

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Date:	Tue, 24 May 2016 07:51:21 +0000
From:	"Li, Liang Z" <liang.z.li@...el.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	"mst@...hat.com" <mst@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"dgilbert@...hat.com" <dgilbert@...hat.com>,
	"amit.shah@...hat.com" <amit.shah@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: RE: [PATCH RFC kernel] balloon: speed up inflating/deflating process

> On 20/05/2016 11:59, Liang Li wrote:
> > +
> > +		sg_init_table(sg, 5);
> > +		sg_set_buf(&sg[0], &flags, sizeof(flags));
> > +		sg_set_buf(&sg[1], &start_pfn, sizeof(start_pfn));
> > +		sg_set_buf(&sg[2], &page_shift, sizeof(page_shift));
> > +		sg_set_buf(&sg[3], &bmap_len, sizeof(bmap_len));
> 
> These four should probably be placed in a single struct and therefore a single
> sg entry.  It might even be faster to place it together with the bitmap, thus
> avoiding the use of indirect descriptors.
> 

Yes, thanks for your suggestion.

> You should also test ballooning of a 64GB guest after filling in the page cache,
> not just ballooning of a freshly booted 4GB guest.  This will give you a much
> more sparse bitmap.  Still, the improvement in sending PFNs to the host are

I will include the test result for that case in next version.


Thanks,

Liang

> impressive.
> 
> Thanks,
> 
> Paolo
> 
> > +		sg_set_buf(&sg[4], vb->page_bitmap +
> > +				 (start_pfn / BITS_PER_LONG), bmap_len);
> > +		virtqueue_add_outbuf(vq, sg, 5, vb, GFP_KERNEL);