linux-kernel - Re: [PATCH 0/5][RFC] Physical PCI slot objects

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Date:	Wed, 14 Nov 2007 15:35:33 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Andi Kleen <andi@...stfloor.org>, Greg KH <greg@...ah.com>,
	Alex Chiang <achiang@...com>, gregkh@...e.de,
	kristen.c.accardi@...el.com, lenb@...nel.org,
	richard.jones2@...com, linux-kernel@...r.kernel.org,
	linux-pci@...ey.karlin.mff.cuni.cz,
	pcihpd-discuss@...ts.sourceforge.net, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 0/5][RFC] Physical PCI slot objects

On Wed, Nov 14, 2007 at 07:17:51AM -0700, Matthew Wilcox wrote:
> On Wed, Nov 14, 2007 at 02:07:56AM +0100, Andi Kleen wrote:
> > It's not only complexity. Each new sysfs entry costs memory.
> > Memory is not free. There should be always a good reason for those.
> 
> It's not a lot of memory; it's one directory and a couple of files for
> each PCI slot in the system.  Even huge systems have maybe 200 slots.
> In order for this to take up as much as one page of ram on a typical PC
> with six slots, this would have to consume 680 bytes per directory.  I
> don't think sysfs is that inefficient (and if it is, maybe this feature
> is not where the problem is, given the 'power' directory per device, the
> 19 files per scsi device, the huge numbers of symlinks, etc).

It becomes much more when someone does a find /sys. dentries are 
expensive. They eventually can get pruned again, but it's still
costly to do that.

-Andi
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