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

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Message-ID: <20180602155324.yrco4xq2yeez2btg@gondor.apana.org.au>
Date:   Sat, 2 Jun 2018 23:53:24 +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, 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 Fri, Jun 01, 2018 at 10:41:31PM -0700, Davidlohr Bueso wrote:
> 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.

Huh? The min_size is a floor for the hash table size.  Some users
may need it because they cannot tolerate the insert-time allocation
or failure.

Your use of min_t against min_size makes absolutely no sense.

Cheers,
-- 
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