linux-kernel - Re: [PATCH] slub: use free_page instead of put

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Date:	Thu, 2 Aug 2012 09:06:41 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Glauber Costa <glommer@...allels.com>
cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: [PATCH] slub: use free_page instead of put_page for freeing
 kmalloc allocation

On Thu, 2 Aug 2012, Glauber Costa wrote:

> diff --git a/mm/slub.c b/mm/slub.c
> index e517d43..9ca4e20 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3453,7 +3453,7 @@ void kfree(const void *x)
>  	if (unlikely(!PageSlab(page))) {
>  		BUG_ON(!PageCompound(page));
>  		kmemleak_free(x);
> -		put_page(page);
> +		__free_pages(page, compound_order(page));

Hmmm... put_page would have called put_compound_page(). which would have
called the dtor function. dtor is set to __free_pages() ok which does
mlock checks and verifies that the page is in a proper condition for
freeing. Then it calls free_one_page().

__free_pages() decrements the refcount and then calls __free_pages_ok().

So we loose the checking and the dtor stuff with this patch. Guess that is
ok?

Acked-by: Christoph Lameter <cl@...ux.com>

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