From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:58522)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <wency@cn.fujitsu.com>) id 1ZfPFB-0000uN-Uf
	for qemu-devel@nongnu.org; Fri, 25 Sep 2015 05:24:46 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <wency@cn.fujitsu.com>) id 1ZfPF8-0003bI-Q4
	for qemu-devel@nongnu.org; Fri, 25 Sep 2015 05:24:41 -0400
Received: from [59.151.112.132] (port=19886 helo=heian.cn.fujitsu.com)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <wency@cn.fujitsu.com>) id 1ZfPF8-0003Zn-FL
	for qemu-devel@nongnu.org; Fri, 25 Sep 2015 05:24:38 -0400
References: <56050489.9010306@cn.fujitsu.com>
	<1443172180-1005-1-git-send-email-den@openvz.org>
	<1443172180-1005-2-git-send-email-den@openvz.org>
From: Wen Congyang <wency@cn.fujitsu.com>
Message-ID: <560512B4.6020406@cn.fujitsu.com>
Date: Fri, 25 Sep 2015 17:24:04 +0800
MIME-Version: 1.0
In-Reply-To: <1443172180-1005-2-git-send-email-den@openvz.org>
Content-Type: text/plain; charset="windows-1252"
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 1/2] migration: bitmap_set is unnecessary
 as bitmap_new uses g_try_malloc0
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: "Denis V. Lunev" <den@openvz.org>
Cc: Amit Shah <amit.shah@redhat.com>, Igor Redko <redkoi@virtuozzo.com>, Juan Quintela <quintela@redhat.com>, qemu-devel@nongnu.org, Anna Melekhova <annam@virtuozzo.com>

On 09/25/2015 05:09 PM, Denis V. Lunev wrote:
> we can omit calling of bitmap_set in migration_bitmap_extend and
> ram_save_setup just after bitmap_new, which properly zeroes memory
> inside.

This patch is wrong. bitmap_set() is set all bits of the memory to 1,
not 0.

> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Igor Redko <redkoi@virtuozzo.com>
> CC: Anna Melekhova <annam@virtuozzo.com>
> CC: Juan Quintela <quintela@redhat.com>
> CC: Amit Shah <amit.shah@redhat.com>
> CC: Wen Congyang <wency@cn.fujitsu.com>
> ---
>  migration/ram.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 7f007e6..a712c68 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1081,7 +1081,6 @@ void migration_bitmap_extend(ram_addr_t old, ram_addr_t new)
>           */
>          qemu_mutex_lock(&migration_bitmap_mutex);
>          bitmap_copy(bitmap, old_bitmap, old);
> -        bitmap_set(bitmap, old, new - old);
>          atomic_rcu_set(&migration_bitmap, bitmap);
>          qemu_mutex_unlock(&migration_bitmap_mutex);
>          migration_dirty_pages += new - old;
> @@ -1146,7 +1145,6 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
>  
>      ram_bitmap_pages = last_ram_offset() >> TARGET_PAGE_BITS;
>      migration_bitmap = bitmap_new(ram_bitmap_pages);
> -    bitmap_set(migration_bitmap, 0, ram_bitmap_pages);
>  
>      /*
>       * Count the total number of pages used by ram blocks not including any
>