linux-kernel - Re: [patch 2/4 -mm] flex_array: add flex_array

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Date:	Mon, 24 Aug 2009 13:29:46 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/4 -mm] flex_array: add flex_array_clear function

On Mon, 24 Aug 2009, Dave Hansen wrote:

> My only worry about this is that it's largely a copy-and-paste of
> flex_array_put().  If we had a function that just returned a pointer to
> 'dst', we could use that in both cases.  
> 
> Couldn't we implement the above with just:
> 
> int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
> {
> 	return flex_array_put(fa, element_nr, &empty_zero_page);
> }
> 

Sure, if you never increase FLEX_ARRAY_PART_SIZE.  Otherwise, doing

static char zero_part[FLEX_ARRAY_PART_SIZE] = {
	[0 ... FLEX_ARRAY_PART_SIZE - 1] = 0
};

and using flex_array_put(fa, element_nr, &zero_part) would work although 
you're trading off cleaner, yet not more efficient, code at the cost of 
FLEX_ARRAY_PART_SIZE wasted memory and memcpy() being slower than 
memset().
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