Message-ID: <44202A2C.505@cosmosbay.com>
Date: Tue, 21 Mar 2006 17:30:36 +0100
From: Eric Dumazet <dada1@cosmosbay.com>
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To: dipankar@in.ibm.com
CC: Jesper Dangaard Brouer <hawk@diku.dk>,
       Robert Olsson <Robert.Olsson@data.slu.se>, jens.laas@data.slu.se,
       hans.liss@its.uu.se, linux-net@vger.kernel.org,
       linux-kernel@vger.kernel.org
Subject: Re: Kernel panic: Route cache, RCU, possibly FIB trie.
References: <Pine.LNX.4.61.0603202234400.27140@ask.diku.dk> <17439.65413.214470.194287@robur.slu.se> <Pine.LNX.4.61.0603211552590.28173@ask.diku.dk> <44201DAF.7090707@cosmosbay.com> <20060321154313.GA9992@in.ibm.com>
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Dipankar Sarma a ?crit :
> On Tue, Mar 21, 2006 at 04:37:19PM +0100, Eric Dumazet wrote:
>> Jesper Dangaard Brouer a ?crit :
>>> There is definitly high memory pressure on this machine!
>>> Slab memory usage, range from 39Mb to 205Mb (at the moment on the 
>>> production servers).
>>>
>> Did you tried 2.6.16 ?
>>
>> It contains changes in kernel/rcupdate.c so that not too many RCU elems are 
>> queued (force_quiescent_state()). So in the case a rt_cache_flush is done, 
>> you have the guarantee all entries are not pushed into rcu at once.
> 
> Well, memory pressure or not, the oopses shouldn't be happening :)
> Perhaps we should look at them before we work around memory
> pressure through the rcu batch tuning stuff in 2.6.16 ?
> 
> One of the oopses looked like the rcu callback function pointer 
> getting corrupted indicating that it was double freed or
> problem with RCU itself.
> 

Yep, but as this is a production server, I believe its owner might want a fast 
way to have it back to life :)

And the RCU change in 2.6.16 is definitly a big improvement when a dump of 
million entries is done :)

If RCU quiescent state is forced, maybe the bug (in the route cache code) will 
trigger faster ?

Eric
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