netdev - Re: [PATCH 3/3] rhashtable: Add nested tables

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Message-ID: <20170207132911.GA14888@gondor.apana.org.au>
Date:   Tue, 7 Feb 2017 21:29:11 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Florian Westphal <fw@...len.de>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Thomas Graf <tgraf@...g.ch>, netdev@...r.kernel.org
Subject: Re: [PATCH 3/3] rhashtable: Add nested tables

On Tue, Feb 07, 2017 at 02:17:28PM +0100, Florian Westphal wrote:
>
> Ok, but why?

Because people expect the hash table insertion to succeed, even
on softirq paths where you cannot vmalloc.

> It seems to add a whole lot of complexity...
> 
> What users can't handle the insert failure case until resize
> has completed?

Users that need to insert on softirq that cannot throttle the
rate.

> Would relaxing the max chain length (until rehash is done) be an
> alternative?

Considering that this is intended for users that cannot throttle
the rate of insertion, I think we'd be much better off just failing
them than sticking them on what will essentially be a linked list.

As people don't like insertion failure, I think this level of
complexity is justified.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt