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

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Date:	Thu, 6 Aug 2015 16:43:15 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	<ian.campbell@...rix.com>, <stefano.stabellini@...citrix.com>,
	<linux-kernel@...r.kernel.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Xen-devel] [PATCH v2 13/20] xen/events: fifo: Make it running
 on 64KB granularity

Hi David,

On 24/07/15 11:36, David Vrabel wrote:
> 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>

Thank you!

>>
>> 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.

I will keep it in mind when I will send a patch to reduce memory waster.

Regards,

-- 
Julien Grall
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