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

KOSAKI Motohiro
2012-10-12T19:28:23Z

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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