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

From: Herbert Xu <herbert@gondor.apana.org.au>
To: Davidlohr Bueso <dave@stgolabs.net>
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: Wed, 30 May 2018 02:04:28 +0800	[thread overview]
Message-ID: <20180529180428.l6yt6ae4oxbgrja6@gondor.apana.org.au> (raw)
In-Reply-To: <20180529170338.7brp2m2k4gfqwf64@linux-n805>

On Tue, May 29, 2018 at 10:03:38AM -0700, Davidlohr Bueso wrote:
> 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.

It doesn't explain it at all.  In fact I don't see why we neeed
three attempts, just do the GFP_NOFAIL as the second and final step.

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