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Date:	Wed, 14 Jan 2015 19:21:33 -0800
From:	John Fastabend <>
To:	Thomas Graf <>
Subject: Re: [net-next PATCH v2 03/12] net: flow: implement flow cache for
 get routines

On 01/14/2015 01:52 PM, Thomas Graf wrote:
> On 01/13/15 at 01:36pm, John Fastabend wrote:
>> I chose rhashtable to get the dynamic resizing. I could use arrays
>> but I don't want to pre-allocate large cache tables when we may
>> never use them.
>> One oddity in the rhashtable implementation is there is no way
>> AFAICS to do delayed free's so we use rcu_sync heavily. This should be
>> fine, get operations shouldn't be a used heavily.
> John, can you please clarify a bit, I'm not sure I understand. Are you
> talking about delayed freeing of the table itself or elements?
> The Netlink usage would be an example of a user with delayed element
> freeing.
> I'm glad to add whatever is required.

Took another look at the netlink code looks like this is the correct
pattern where the call_rcu implements the delayed freeing after a grace

	rhashtable_remove(&my_hash, &my_obj->rhash_head);


	call_rcu(&my_obj->rcu, deferred_my_obj_free);

anyways it looks like it is there no problem after all and I don't
recall what I was thinking thanks for bearing with me. I'll convert
this code to avoid the over-use of rcu_sync.


John Fastabend         Intel Corporation
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