linux-kernel - Re: [PATCH/RFC] MM slub: add a sysfs entry to show the calculated number of fallback slabs

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Message-ID: <alpine.DEB.2.00.1011121043250.5830@chino.kir.corp.google.com>
Date:	Fri, 12 Nov 2010 10:46:51 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Richard Kennedy <richard@....demon.co.uk>
cc:	Pekka Enberg <penberg@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH/RFC] MM slub: add a sysfs entry to show the calculated
 number of fallback slabs

On Fri, 12 Nov 2010, Richard Kennedy wrote:

> Add a slub sysfs entry to show the calculated number of fallback slabs.
> 
> Using the information already available it is straightforward to
> calculate the number of fallback & full size slabs. We can then track
> which slabs are particularly effected by memory fragmentation and how
> long they take to recover. 
> 
> There is no change to the mainline code, the calculation is only
> performed on request, and the value is available without having to
> enable CONFIG_SLUB_STATS.  
> 

I don't see why this information is generally useful unless debugging an 
issue where statistics are already needed such as ALLOC_SLOWPATH and 
ALLOC_SLAB, so it CONFIG_SLUB_STATS can be enabled to also track 
ORDER_FALLBACK.  All stats can be cleared by writing a '0' to its sysfs 
stats file so you can collect statistics for various workloads without 
rebooting (after doing a forced shrink, for example).
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