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

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Message-ID: <20180529170338.7brp2m2k4gfqwf64@linux-n805>
Date:   Tue, 29 May 2018 10:03:38 -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,
        guillaume.knispel@...ersonicimagine.com, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 2/6] lib/rhashtable: guarantee initial hashtable
 allocation

On Mon, 28 May 2018, Herbert Xu 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;
>> +
>> +		tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
>> +		if (tbl == NULL)
>> +			tbl = bucket_table_alloc_retry(ht, size, GFP_KERNEL);
>> +	}
>
>Perhaps you should also explain here why we don't just try the
>minimum size with __GFP_NOFAIL as the second step rather than the
>third.

Please see the comment above, I try to explain the rationale.

Thanks,
Davidlohr