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

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Date:   Wed, 30 May 2018 02:04:28 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Davidlohr Bueso <dave@...olabs.net>
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 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@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt