linux-kernel - Re: [Xen-devel] [PATCH] Input: xen-kbdfront - free grant table entry in xenkbd_disconnect

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Message-ID: <20141016203719.GB38361@dtor-ws>
Date:	Thu, 16 Oct 2014 13:37:19 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	hansechang@...il.com, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xen.org,
	Chang Huaixin <huaixin.chx@...baba-inc.com>,
	jinsong.liu@...baba-inc.com, Ian.Campbell@...citrix.com,
	dgdegra@...ho.nsa.gov, boris.ostrovsky@...cle.com
Subject: Re: [Xen-devel] [PATCH] Input: xen-kbdfront - free grant table entry
 in xenkbd_disconnect_backend

On Thu, Oct 16, 2014 at 05:01:09PM +0100, David Vrabel wrote:
> On 16/10/14 02:46, hansechang@...il.com wrote:
> > From: Chang Huaixin <huaixin.chx@...baba-inc.com>
> > 
> > xenkbd_disconnect_backend doesn't free grant table entry.
> > This bug affects live migration.
> > 
> > xenkbd_disconnect_backend uses gnttab_end_foreign_access_ref
> > to handle grant table entry which doesn't really free an entry.
> > 
> > Thus every time we do xenkbd_resume, grant table entry increses
> > by one. As an grant table entry occupies 8 bytes, an grant table
> > page has at most 512 entries. Every 512 times we do xenkdb_resume,
> > grant table pages increses by one.
> > 
> > After around 3500 times of live migration, grant table pages
> > will increase by 7, causing too many pages to populate and hitting
> > max_pages limit when assigning pages.Thus assign_pages will fail,
> > so will live migration.
> 
> Acked-by: David Vrabel <david.vrabel@...rix.com>
> 
> This need to be send to the input subsystem maintainers.

Applied, thank you.

-- 
Dmitry
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