Re: [PATCH ipvs-next] ipvs: Remove rcu_read_unlock();rcu_read_lock();

To: Julian Anastasov <ja@xxxxxx>
Subject: Re: [PATCH ipvs-next] ipvs: Remove rcu_read_unlock();rcu_read_lock();
Cc: Simon Horman <horms@xxxxxxxxxxxx>, Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>, lvs-devel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, netfilter-devel@xxxxxxxxxxxxxxx, Wensong Zhang <wensong@xxxxxxxxxxxx>
From: Hans Schillstrom <hans@xxxxxxxxxxxxxxx>
Date: Thu, 25 Apr 2013 11:05:26 +0200
On Thu, 2013-04-25 at 11:15 +0300, Julian Anastasov wrote:
>       Hello,
> On Thu, 25 Apr 2013, Simon Horman wrote:
> > It is unclear to me that there is any utility in the following:
> > 
> >      rcu_read_unlock();
> >      rcu_read_lock();
>       I thought it is a good idea for fixed hash table
> of IP_VS_TAB_BITS=20. May be if guarded by
>       if (!((++idx) & 4095))
> to reduce its rate to 256 (with idx++ removed from the for loop) ?
>       Netfilter has no such logic for nf_conntrack because
> it has limit of 16384 rows. Not sure how fatal is to try 1048576
> empty rows under RCU lock for such rare operations as
> connection listing. OTOH, ip_vs_conn_array() needs to
> seek at some initial position, so it can skip many
> entries if reading table with many conns, for example,
> 1048576 rows * 16 conns per row, we will need to
> touch 16777216 conns under lock. Not sure what is the
> best practice for such cases.

My opinion is to keep it, people tends to do such "rare" things.
It's not unusual with 256k - 1M rows... 


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