linux-kernel - Re: [PATCH 2/3] Sysfs: Allow directories to be populated dynamically

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Date:	Fri, 30 Oct 2009 17:06:36 +0100
From:	Tejun Heo <teheo@...e.de>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH 2/3] Sysfs: Allow directories to be populated	dynamically

Hello,

Matthew Wilcox wrote:
>> In this particular case, the trade off is actually much worse because
>> sysfs_dirent is being increased but the only one which is seeing any
>> kind of memory usage drop is the new msi-x code.  Given that there can
>> be only a handful of msi-x controllers even in a fairly large system,
>> I don't think memory usage will be reduced in any meaningful way even
>> on affected systems and if you think about large systems with
>> thousands and tens of thousands block devices, the bloat in
>> sysfs_dirent will waste a lot of memory.
> 
> Every attribute sees a drop in memory usage.  I think I saw about 30%
> fewer dirents created on boot with this laptop.  Why not try this patch
> on one of your machines and see the difference?

Heh... Sorry, I'm still travelling so testing is a bit difficult but
even if you reduce the number of dirents by 30% if you add three
pointers worth of memory to each sysfs_dirent, I don't think it will
amount to any meaningful amount of memory usage drop and given that
sysfs_dirent can be reduced further in size with some tricks, I think
that would be the better way to reduce memory footprint.

Thanks.

-- 
tejun
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