linux-kernel - Re: [PATCH v2 13/20] xen/events: fifo: Make it running on 64KB granularity

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Message-ID: <55B21527.4010601@citrix.com>
Date:	Fri, 24 Jul 2015 11:36:23 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Julien Grall <julien.grall@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	<linux-arm-kernel@...ts.infradead.org>, <ian.campbell@...rix.com>,
	<stefano.stabellini@...citrix.com>, <linux-kernel@...r.kernel.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH v2 13/20] xen/events: fifo: Make it running on 64KB granularity

On 09/07/15 21:42, Julien Grall wrote:
> Only use the first 4KB of the page to store the events channel info. It
> means that we will wast 60KB every time we allocate page for:
>      * control block: a page is allocating per CPU
>      * event array: a page is allocating everytime we need to expand it

Reviewed-by: David Vrabel <david.vrabel@...rix.com>
> 
> I think we can reduce the memory waste for the 2 areas by:
> 
>     * control block: sharing between multiple vCPUs. Although it will
>     require some bookkeeping in order to not free the page when the CPU
>     goes offline and the other CPUs sharing the page still there
> 
>     * event array: always extend the array event by 64K (i.e 16 4K
>     chunk). That would require more care when we fail to expand the
>     event channel.

I would extend it by 4 KiB each time but only allocate a new page every
16 times.  This minimizes the resources used in Xen.

David
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