linux-kernel - Re: [PATCH 0/4] De-couple sysfs memory directories from memory sections

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Date:	Thu, 20 Jan 2011 09:09:01 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Greg KH <greg@...ah.com>
Cc:	Nathan Fontenot <nfont@...tin.ibm.com>, linux-mm@...ck.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Robin Holt <holt@....com>
Subject: Re: [PATCH 0/4] De-couple sysfs memory directories from memory
 sections

On Thu, 2011-01-20 at 08:45 -0800, Greg KH wrote:
> On Thu, Jan 20, 2011 at 10:36:40AM -0600, Nathan Fontenot wrote:
> > The root of this issue is in sysfs directory creation. Every time
> > a directory is created a string compare is done against sibling
> > directories ( see sysfs_find_dirent() ) to ensure we do not create 
> > duplicates.  The list of directory nodes in sysfs is kept as an
> > unsorted list which results in this being an exponentially longer
> > operation as the number of directories are created.
> 
> Again, are you sure about this?  I thought we resolved this issue in the
> past, but you were going to check it.  Did you?

Just to be clear, simply reducing the number of kobjects can make these
patches worthwhile on their own.  I originally figured that the
SECTION_SIZE would go up over time as systems got larger, and _that_
would keep the number of sections and number of sysfs objects down.
Well, that turned out to be wrong, and we're eating up a ton of memory
now.  We can't fix the SECTION_SIZE easily, but we can reduce the number
of kobjects that we need to track the sections.  *That* is the main
benefit I see from these patches.

I think there's a problem worth fixing, even ignoring the directory
creation issue (if it still exists).

-- Dave

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