Date: Thu, 2 Aug 2012 09:06:41 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
To: Glauber Costa <glommer@parallels.com>
cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
        linux-mm@kvack.org, David Rientjes <rientjes@google.com>,
        Pekka Enberg <penberg@kernel.org>
Subject: Re: [PATCH] slub: use free_page instead of put_page for freeing
 kmalloc allocation
In-Reply-To: <1343913065-14631-1-git-send-email-glommer@parallels.com>
Message-ID: <alpine.DEB.2.00.1208020902390.23049@router.home>
References: <1343913065-14631-1-git-send-email-glommer@parallels.com>
User-Agent: Alpine 2.00 (DEB 1167 2008-08-23)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1056
Lines: 30

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@linux.com>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/