linux-kernel - Re: [PATCH 2/3] staging: lustre: lnet: Allocate MEs and small MDs in own kmem

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Message-ID: <B6A45EE2-D900-4578-AC42-4F5933F945DA@intel.com>
Date:	Fri, 10 Jun 2016 15:25:28 +0000
From:	"Faccini, Bruno" <bruno.faccini@...el.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	James Simmons <jsimmons@...radead.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"Dilger, Andreas" <andreas.dilger@...el.com>,
	"Drokin, Oleg" <oleg.drokin@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lustre Development List <lustre-devel@...ts.lustre.org>
Subject: Re: [PATCH 2/3] staging: lustre: lnet: Allocate MEs and small MDs
 in own kmem_caches

Hello,
The intent of this patch is not to solve the corruptions for sure, but only to avoid the concerned MEs/small-MDs LNet structs to be quite frequently impacted due to their high allocation/free rate. This may also possibly help to save cycles due to high usage and contention when using a generic kmem_cache (when they stay separate from others, thanks for the precision!).
Bye,
Bruno.

> Le Jun 10, 2016 à 03:28, Greg Kroah-Hartman <gregkh@...uxfoundation.org> a écrit :
> 
> On Thu, Jun 09, 2016 at 06:45:46PM -0400, James Simmons wrote:
>> From: Bruno Faccini <bruno.faccini@...el.com>
>> 
>> As part of LU-3848 and LU-4330, it has been discovered that LNET
>> MEs and small MDs (<=128 Bytes) are allocated in <size-128> kmem_cache
>> and thus can suffer quite frequent corruptions, from other modules or
>> Kernel parts, that occur there. To avoid this, MEs and small-MDs
>> specific kmem_cache have been created.
> 
> What?  Who corrupts them?  That shouldn't be possible, and on some
> systems, even if you do ask for a separate slab, it will be merged
> togther with others of the same size.  So this patch doesn't do all that
> much.
> 
> I think you are having some other problem here, changing to a separate
> memory cache shouldn't solve corruption issues.
> 
> sorry,
> 
> greg k-h

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