Re: [PATCH 2/6] lib/rhashtable: guarantee initial hashtable allocation

From: Davidlohr Bueso <dave@stgolabs.net>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: akpm@linux-foundation.org, torvalds@linux-foundation.org,
	tgraf@suug.ch, manfred@colorfullife.com,
	guillaume.knispel@supersonicimagine.com,
	linux-api@vger.kernel.org, linux-kernel@vger.kernel.org,
	Davidlohr Bueso <dbueso@suse.de>
Subject: Re: [PATCH 2/6] lib/rhashtable: guarantee initial hashtable allocation
Date: Tue, 29 May 2018 09:42:31 -0700	[thread overview]
Message-ID: <20180529164231.yoj57nqhghtmy54v@linux-n805> (raw)
In-Reply-To: <20180528100237.needq2u5e3v2n642@gondor.apana.org.au>

On Mon, 28 May 2018, Herbert Xu wrote:

>On Thu, May 24, 2018 at 02:11:31PM -0700, Davidlohr Bueso wrote:
>>
>> +	/*
>> +	 * This is api initialization and thus we need to guarantee the
>> +	 * initial rhashtable allocation. Upon failure, retry with a
>> +	 * smallest possible size, otherwise we exhaust our options with
>> +	 * __GFP_NOFAIL.
>> +	 */
>>  	tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
>> -	if (tbl == NULL)
>> -		return -ENOMEM;
>> +	if (unlikely(tbl == NULL)) {
>> +		size = HASH_MIN_SIZE;
>
>You should also take min_size into account.  Yes I know the current
>code ignores it unless you also set nelem_hint.  But that's just a
>bug.

For the sake of simplicity, Linus suggested directly using HASH_MIN_SIZE
such that we have a single fallback.

Thanks,
Davidlohr