Re: [Qemu-devel] [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate process

[Li, Liang Z]

> Subject: Re: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate
> process
> 
> On Wed, Jul 27, 2016 at 09:03:21AM -0700, Dave Hansen wrote:
> > On 07/26/2016 06:23 PM, Liang Li wrote:
> > > + vb->pfn_limit = VIRTIO_BALLOON_PFNS_LIMIT;
> > > + vb->pfn_limit = min(vb->pfn_limit, get_max_pfn());
> > > + vb->bmap_len = ALIGN(vb->pfn_limit, BITS_PER_LONG) /
> > > +          BITS_PER_BYTE + 2 * sizeof(unsigned long);
> > > + hdr_len = sizeof(struct balloon_bmap_hdr);
> > > + vb->bmap_hdr = kzalloc(hdr_len + vb->bmap_len, GFP_KERNEL);
> >
> > This ends up doing a 1MB kmalloc() right?  That seems a _bit_ big.
> > How big was the pfn buffer before?
> 
> 
> Yes I would limit this to 1G memory in a go, will result in a 32KByte bitmap.
> 
> --
> MST

Limit to 1G is bad for the performance, I sent you the test result several 
weeks ago.

Paste it bellow:
------------------------------------------------------------------------------------------------------------------------
About the size of page bitmap, I have test the performance of filling the 
balloon to 15GB with a
 16GB RAM VM.

===============================
32K Byte (cover 1GB of RAM)

Time spends on inflating: 2031ms
---------------------------------------------
64K Byte (cover 2GB of RAM)

Time spends on inflating: 1507ms
--------------------------------------------
512K Byte (cover 16GB of RAM)

Time spends on inflating: 1237ms
================================

If possible, a big bitmap is better for performance.

Liang