linux-kernel - Re: [PATCH 2/5] lib/rhashtable: guarantee initial hashtable allocation

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Message-ID: <20180602054131.ta7ligrfwbgvemfv@linux-r8p5>
Date:   Fri, 1 Jun 2018 22:41:31 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
        tgraf@...g.ch, manfred@...orfullife.com, mhocko@...nel.org,
        guillaume.knispel@...ersonicimagine.com, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 2/5] lib/rhashtable: guarantee initial hashtable
 allocation

On Sat, 02 Jun 2018, Herbert Xu wrote:
>>  	tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
>> -	if (tbl == NULL)
>> -		return -ENOMEM;
>> +	if (unlikely(tbl == NULL)) {
>> +		size = min_t(u16, ht->p.min_size, HASH_MIN_SIZE);
>
>You mean max_t?

Not really. I considered some of the users to set quite a large min_size
(such as 1024 buckets). The min() makes sense to me in that it's the smallest
possible value. If memory later becomes available and the hashtable is resized
to a more appropriate value, couldn't any issues regarding collisions not be dealt
with organically? And we've agreed that allocating a tiny table is the
least of our problems.

Thanks,
Davidlohr