Re: [PATCH 5/10] memory-hotplug : memory-hotplug: check page type in get_page_bootmem

From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: linux-s390@vger.kernel.org, linux-ia64@vger.kernel.org,
	wency@cn.fujitsu.com, len.brown@intel.com,
	linux-acpi@vger.kernel.org, linux-sh@vger.kernel.org,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	cmetcalf@tilera.com, linux-mm@kvack.org, minchan.kim@gmail.com,
	rientjes@google.com, sparclinux@vger.kernel.org, cl@linux.com,
	linuxppc-dev@lists.ozlabs.org, akpm@linux-foundation.org,
	liuj97@gmail.com
Subject: Re: [PATCH 5/10] memory-hotplug : memory-hotplug: check page type in get_page_bootmem
Date: Fri, 12 Oct 2012 15:28:23 -0400	[thread overview]
Message-ID: <CAHGf_=raSH5C8ye90F1PLZ8mGQUGggB=J0HYU8UhkKVDTV5JXQ@mail.gmail.com> (raw)
In-Reply-To: <506E46B6.3060502@jp.fujitsu.com>

On Thu, Oct 4, 2012 at 10:32 PM, Yasuaki Ishimatsu
<isimatu.yasuaki@jp.fujitsu.com> wrote:
> The function get_page_bootmem() may be called more than one time to the same
> page. There is no need to set page's type, private if the function is not
> the first time called to the page.
>
> Note: the patch is just optimization and does not fix any problem.
>
> CC: David Rientjes <rientjes@google.com>
> CC: Jiang Liu <liuj97@gmail.com>
> CC: Len Brown <len.brown@intel.com>
> CC: Christoph Lameter <cl@linux.com>
> Cc: Minchan Kim <minchan.kim@gmail.com>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> CC: Wen Congyang <wency@cn.fujitsu.com>
> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
> ---
>  mm/memory_hotplug.c |   15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>
> Index: linux-3.6/mm/memory_hotplug.c
> ===================================================================
> --- linux-3.6.orig/mm/memory_hotplug.c  2012-10-04 18:29:58.284676075 +0900
> +++ linux-3.6/mm/memory_hotplug.c       2012-10-04 18:30:03.454680542 +0900
> @@ -95,10 +95,17 @@ static void release_memory_resource(stru
>  static void get_page_bootmem(unsigned long info,  struct page *page,
>                              unsigned long type)
>  {
> -       page->lru.next = (struct list_head *) type;
> -       SetPagePrivate(page);
> -       set_page_private(page, info);
> -       atomic_inc(&page->_count);
> +       unsigned long page_type;
> +
> +       page_type = (unsigned long)page->lru.next;

If I understand correctly, page->lru.next might be uninitialized yet.

Moreover, I have no seen any good effect in this patch. I don't understand
why we need to increase code complexity.

> +       if (page_type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
> +           page_type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE){
> +               page->lru.next = (struct list_head *)type;
> +               SetPagePrivate(page);
> +               set_page_private(page, info);
> +               atomic_inc(&page->_count);
> +       } else
> +               atomic_inc(&page->_count);
>  }
>
>  /* reference to __meminit __free_pages_bootmem is valid
>
> --
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