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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <F2CBF3009FA73547804AE4C663CAB28E04216308@shsmsx102.ccr.corp.intel.com>
Date:	Tue, 2 Aug 2016 00:28:19 +0000
From:	"Li, Liang Z" <liang.z.li@...el.com>
To:	"Hansen, Dave" <dave.hansen@...el.com>,
	"Michael S. Tsirkin" <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>,
	"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: [virtio-dev] Re: [PATCH v2 repost 4/7] virtio-balloon: speed up
 inflate/deflate process

> > It's only small because it makes you rescan the free list.
> > So maybe you should do something else.
> > I looked at it a bit. Instead of scanning the free list, how about
> > scanning actual page structures? If page is unused, pass it to host.
> > Solves the problem of rescanning multiple times, does it not?
> 
> FWIW, I think the new data structure needs some work.
> 
> Before, we had a potentially very long list of 4k areas.  Now, we've just got a
> very large bitmap.  The bitmap might not even be very dense if we are
> ballooning relatively few things.
> 
> Can I suggest an alternate scheme?  I think you actually need a hybrid
> scheme that has bitmaps but also allows more flexibility in the pfn ranges.
> The payload could be a number of records each containing 3 things:
> 
> 	pfn, page order, length of bitmap (maybe in powers of 2)
> 
> Each record is followed by the bitmap.  Or, if the bitmap length is 0,
> immediately followed by another record.  A bitmap length of 0 implies a
> bitmap with the least significant bit set.  Page order specifies how many
> pages each bit represents.
> 
> This scheme could easily encode the new data structure you are proposing
> by just setting pfn=0, order=0, and a very long bitmap length.  But, it could
> handle sparse bitmaps much better *and* represent large pages much more
> efficiently.
> 
> There's plenty of space to fit a whole record in 64 bits.

I like your idea and it's more flexible, and it's very useful if we want to optimize the
page allocating stage further. I believe the memory fragmentation will not be very
serious, so the performance won't be too bad in the worst case.

Thanks!
Liang