From owner-freebsd-questions@freebsd.org  Sun Jan 21 21:22:07 2018
Return-Path: <owner-freebsd-questions@freebsd.org>
Delivered-To: freebsd-questions@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id EF670EBC1EB
 for <freebsd-questions@mailman.ysv.freebsd.org>;
 Sun, 21 Jan 2018 21:22:07 +0000 (UTC)
 (envelope-from mail@kkoenig.net)
Received: from mx1.outerhaven.de (mx1.outerhaven.de [81.14.236.89])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id 8357E7D09F
 for <freebsd-questions@freebsd.org>; Sun, 21 Jan 2018 21:22:06 +0000 (UTC)
 (envelope-from mail@kkoenig.net)
Received: from [192.168.2.113] (shadow-moses.lan [192.168.2.113])
 by mx1.outerhaven.de (OpenSMTPD) with ESMTPSA id 8d65b70b
 TLS version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NO
 for <freebsd-questions@freebsd.org>;
 Sun, 21 Jan 2018 22:15:23 +0100 (CET)
To: freebsd-questions@freebsd.org
From: =?UTF-8?Q?Karsten_K=c3=b6nig?= <mail@kkoenig.net>
Subject: Question about 'anonymous' UMA zones
Message-ID: <8153a344-bd74-620c-3e05-47a28852beb6@kkoenig.net>
Date: Sun, 21 Jan 2018 22:15:23 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.5.2
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Language: de-DE
Content-Transfer-Encoding: 7bit
X-BeenThere: freebsd-questions@freebsd.org
X-Mailman-Version: 2.1.25
Precedence: list
List-Id: User questions <freebsd-questions.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/freebsd-questions>, 
 <mailto:freebsd-questions-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-questions/>
List-Post: <mailto:freebsd-questions@freebsd.org>
List-Help: <mailto:freebsd-questions-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/freebsd-questions>, 
 <mailto:freebsd-questions-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sun, 21 Jan 2018 21:22:08 -0000

Hello y'all,

I just played a little bit with the zone allocator of the FreeBSD kernel
and observed the following: All 'anonymous' zones (is this the
appropriate term?) with a size smaller than 512 Bytes have no slabs:

# vmstat -z
ITEM                   SIZE  LIMIT     USED     FREE      REQ FAIL SLEEP
...
16:                      16,      0,       0,       0,       0,   0,   0

32:                      32,      0,       0,       0,       0,   0,   0

64:                      64,      0,       0,       0,       0,   0,   0

128:                    128,      0,       0,       0,       0,   0,   0

256:                    256,      0,       0,       0,       0,   0,   0

512:                    512,      0,    7906,      70,   97681,   0,   0
...

I would like to know why this is the case; can someone explain this to
me? What happens if I allocate e.g. a 256 Byte buffer?

Best,

Karsten