linux-kernel - RE: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate process

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Message-ID: <F2CBF3009FA73547804AE4C663CAB28E04213E5D@shsmsx102.ccr.corp.intel.com>
Date:	Thu, 28 Jul 2016 03:30:09 +0000
From:	"Li, Liang Z" <liang.z.li@...el.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>,
	"Hansen, Dave" <dave.hansen@...el.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>,
	"dgilbert@...hat.com" <dgilbert@...hat.com>,
	"quintela@...hat.com" <quintela@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Vlastimil Babka" <vbabka@...e.cz>,
	Mel Gorman <mgorman@...hsingularity.net>,
	"Paolo Bonzini" <pbonzini@...hat.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Amit Shah <amit.shah@...hat.com>
Subject: RE: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate
 process

> 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