netdev - Re: dev: Reclaim network device indexes

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Message-Id: <20170620.124250.956500694842302363.davem@davemloft.net>
Date:   Tue, 20 Jun 2017 12:42:50 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     serhe.popovych@...il.com
Cc:     netdev@...r.kernel.org, stephen@...workplumber.org
Subject: Re: dev: Reclaim network device indexes

From: Serhey Popovych <serhe.popovych@...il.com>
Date: Fri, 16 Jun 2017 19:39:34 +0300

> While making dev_new_index() return zero on overrun prevents
> from infinite loop, there is no way to recovery mechanisms
> since namespace ifindex only increases and never reused
> from released network devices.
> 
> To address this we introduce dev_free_index() helper which
> is used to reclaim released network device index when it is
> smaller than last allocated index in namespace.
> 
> This also has positive side effect for equal distribution
> of network devices per buckets in index hash table. That
> positively affects performance of dev_get_by_index() family.
> 
> Signed-off-by: Serhey Popovych <serhe.popovych@...il.com>

You haven't explained why the current behavior is undesirable,
and why we want reuse.

I don't think we want at all for anything to rely on ifindexes
being allocated one way or another.

Yes, I understand that hash table argument, but that can be solved
other ways.  And what you're talking about is more of an error case
not a normal case.