linux-kernel - Re: [PATCH -mm] relayfs: support larger relay buffer take 3

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Message-Id: <20080416134805.fdd139c1.akpm@linux-foundation.org>
Date:	Wed, 16 Apr 2008 13:48:05 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	penberg@...helsinki.fi, zanussi@...cast.net, dwilder@...ibm.com,
	systemtap@...rces.redhat.com, linux-kernel@...r.kernel.org,
	tzanussi@...il.com
Subject: Re: [PATCH -mm] relayfs: support larger relay buffer take 3

On Wed, 16 Apr 2008 15:51:56 -0400
Masami Hiramatsu <mhiramat@...hat.com> wrote:

> +static struct page **relay_alloc_page_array(unsigned int n_pages)
> +{
> +	struct page **array;
> +	unsigned int pa_size = n_pages * sizeof(struct page *);
> +
> +	if (pa_size > PAGE_SIZE) {
> +		array = vmalloc(pa_size);
> +		if (array)
> +			memset(array, 0, pa_size);
> +	} else {
> +		array = kcalloc(n_pages, sizeof(struct page *), GFP_KERNEL);
> +	}
> +	return array;
> +}

It's a bit odd to multiply n_pages*sizeof() and to then call kcalloc(),
which needs to do the same multiplication.

The compiler will presumably optimise that away, but still, how about this?

--- a/kernel/relay.c~relayfs-support-larger-relay-buffer-take-3-cleanup
+++ a/kernel/relay.c
@@ -71,14 +71,14 @@ static struct vm_operations_struct relay
 static struct page **relay_alloc_page_array(unsigned int n_pages)
 {
 	struct page **array;
-	unsigned int pa_size = n_pages * sizeof(struct page *);
+	size_t pa_size = n_pages * sizeof(struct page *);
 
 	if (pa_size > PAGE_SIZE) {
 		array = vmalloc(pa_size);
 		if (array)
 			memset(array, 0, pa_size);
 	} else {
-		array = kcalloc(n_pages, sizeof(struct page *), GFP_KERNEL);
+		array = kzalloc(pa_size, GFP_KERNEL);
 	}
 	return array;
 }
_


size_t is strictly the correct type for pa_size here.  Even though
vmalloc() takes a ulong.

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