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

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Date:	Thu, 16 Oct 2014 17:01:09 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	<hansechang@...il.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xen.org>
CC:	Chang Huaixin <huaixin.chx@...baba-inc.com>,
	<jinsong.liu@...baba-inc.com>, <Ian.Campbell@...citrix.com>,
	<david.vrabel@...rix.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 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.

David
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