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

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Message-ID: <4A9FCDF7.1090700@corp.free.fr>
Date:	Thu, 03 Sep 2009 16:08:55 +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

Trond Myklebust wrote:
> On Thu, 2009-09-03 at 15:39 +0200, Yohan wrote:
>   
>>> 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.
>>     
> OK, so 16 hash buckets are likely to be filled with ~10^6 entries each.
> I can see that might be a performance issue...
>
> So afaics, you did try adjusting the hashtable size. How much larger
> does it have to be before you start to get acceptable performance? If it
> solves your problem we could make hash table sizes adjustable via a
> module parameter, for instance.
>   
I run now with a value of 12, and it's great for me...

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