linux-kernel - Re: [PATCH 5/10] memory-hotplug : memory-hotplug: check page type in get_page

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Message-ID: <CAHGf_=raSH5C8ye90F1PLZ8mGQUGggB=J0HYU8UhkKVDTV5JXQ@mail.gmail.com>
Date:	Fri, 12 Oct 2012 15:28:23 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-ia64@...r.kernel.org, cmetcalf@...era.com,
	sparclinux@...r.kernel.org, rientjes@...gle.com, liuj97@...il.com,
	len.brown@...el.com, cl@...ux.com, minchan.kim@...il.com,
	akpm@...ux-foundation.org, wency@...fujitsu.com
Subject: Re: [PATCH 5/10] memory-hotplug : memory-hotplug: check page type in get_page_bootmem

On Thu, Oct 4, 2012 at 10:32 PM, Yasuaki Ishimatsu
<isimatu.yasuaki@...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@...gle.com>
> CC: Jiang Liu <liuj97@...il.com>
> CC: Len Brown <len.brown@...el.com>
> CC: Christoph Lameter <cl@...ux.com>
> Cc: Minchan Kim <minchan.kim@...il.com>
> CC: Andrew Morton <akpm@...ux-foundation.org>
> CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> CC: Wen Congyang <wency@...fujitsu.com>
> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@...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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