linux-kernel - Re: VM issue causing high CPU loads

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Message-ID: <4A9FC719.9020104@corp.free.fr>
Date:	Thu, 03 Sep 2009 15:39:37 +0200
From:	Yohan <ytordjman@...p.free.fr>
To:	Trond Myklebust <trond.myklebust@....uio.no>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	Neil Brown <neilb@...e.de>,
	"J. Bruce Fields" <bfields@...ldses.org>, mikevs@...all.net
Subject: Re: VM issue causing high CPU loads


>>> I did only:
>>>
>>> --- linux-2.6.27.21/include/linux/sunrpc/auth.h	2009-03-23 23:04:09.000000000 +0100
>>> +++ linux-2.6.27.21/include/linux/sunrpc/auth.h	2009-05-19 16:02:35.000000000 +0200
>>> @@ -62,8 +62,12 @@ 
>>>   */
>>> - #define RPC_CREDCACHE_HASHBITS	4
>>> + #define RPC_CREDCACHE_HASHBITS	12
>>>
>>>
>>> And i test it in prod since sunday: i only have 36% of one core used by 
>>> system
>>> versus more than 3 cores used by system in another server that did a 
>>> drop_caches at morning...
>>>       
>> OK, but it's still pretty bad.  Let's tell the NFS guys.
>>
>> In http://bugzilla.kernel.org/show_bug.cgi?id=14024 we appear to have a
>> major meltdown caused by the linear search in
>> rpcauth_lookup_credcache() with Yohan's workload.
>>     
> OK. Could we please have some more details about the actual workload involved here?
>   
I add a new server CPU graph and 60s readprofile on the bugzilla

> As far as I can see, there is no RPCSEC_GSS involved, so credentials
> should never expire. They will be reused as long as processes aren't
> switching between thousands and thousands of different combinations of
> uid, gid and groups.
My servers are imap servers.
Foreach user (~15 million) it have a specific uid over ~10 nfs netapp 
storage.

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