linux-kernel - Re: [PATCH 1/3] Make /dev/urandom scalable

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Date:	Wed, 23 Sep 2015 23:54:47 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Andi Kleen <andi@...stfloor.org>, tytso@....edu,
	linux-kernel@...r.kernel.org, kirill.shutemov@...ux.intel.com,
	herbert@...dor.apana.org.au, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/3] Make /dev/urandom scalable

> > +{
> > +	struct entropy_store *pool = &nonblocking_pool;
> > +
> > +	/*
> > +	 * Non node 0 pools may take longer to initialize. Keep using
> > +	 * the boot nonblocking pool while this happens.
> > +	 */
> > +	if (nonblocking_node_pool)
> > +		pool = nonblocking_node_pool[numa_node_id()];
> > +	if (!pool->initialized)
> > +		pool = &nonblocking_pool;
> > +	return pool;
> > +}
> 
> I assume this can't get called concurrently with rand_initialize
> (otherwise pool may be NULL even if nonblocking_node_pool is non-NULL). 

Yes. I can move the assignment to the global last and add a memory
barrier.

> > +	char name[40];
> > +
> > +	nonblocking_node_pool = kzalloc(num_nodes * sizeof(void *),
> > +					GFP_KERNEL|__GFP_NOFAIL);
> > +
> 
> Why kzalloc, when you immediately initialize all elements? New uses of
> __GFP_NOFAIL seem to be frowned upon. How hard would it be to just fall
> back to only using the single statically allocated pool?

It's already doing that.

> 
> Does rand_initialize get called before or after other initialization
> code updates node_possible_map to reflect the actual possible number of
> nodes? If before, won't we be wasting a lot of memory (not to mention
> that we then might as well allocate all the nonblocking pools statically
> based on MAX_NUMNODES).

I'll check.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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