linux-kernel - Re: Idea for reducing sysfs memory usage

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Date:	Tue, 16 Feb 2016 17:44:54 -0700
From:	David Ahern <dsa@...ulusnetworks.com>
To:	Edward Cree <ec429@...tab.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Idea for reducing sysfs memory usage

On 2/16/16 5:37 PM, Edward Cree wrote:
> On 16/02/16 23:55, Greg Kroah-Hartman wrote:
>> On Tue, Feb 16, 2016 at 11:46:49PM +0000, Edward Cree wrote:
>>> Sorry if this has been suggested before, but if so I couldn't find it.
>>> Short version: could a sysfs dir reference a list of default attributes
>>> rather than having to instantiate them all?
>> Shorter version, why do you think it is?  :)
>>
>> Have you done some testing of the amount of memory that sysfs entries
>> consume and found any problems with it?
> Two reasons:
> a) in his netdev1.1 talk "Scaling the Number of Network Interfaces on
> Linux",
>     David Ahern claimed a memory overhead of (iirc) about 45kB per
> netdevice,
>     of which he attributed (again, iirc) about 20kB to sysfs entries. He
> also
>     indicated that this was a problem for his use case.  (My apologies to
>     David if I've misrepresented him.  CCed him so he can correct me.)

Close enough. :-)

I analyzed memory allocations for the creation of a dummy netdevice. All 
total 36,450 bytes were requested resulting in 43,944 bytes allocated. 
Of that kobject and sysfs is 14,568. So kobject and sysfs is roughly 1/3 
the memory overhead of a netdevice and is also a significant overhead in 
the time to create the netdevice.

David