From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx207.postini.com [74.125.245.207]) by kanga.kvack.org (Postfix) with SMTP id 415806B0044 for ; Fri, 23 Mar 2012 05:00:23 -0400 (EDT) Received: by obbta14 with SMTP id ta14so2898718obb.14 for ; Fri, 23 Mar 2012 02:00:22 -0700 (PDT) Message-ID: <4F6C3B7F.1070705@gmail.com> Date: Fri, 23 Mar 2012 16:59:43 +0800 From: bill4carson MIME-Version: 1.0 Subject: Re: Why memory.usage_in_bytes is always increasing after every mmap/dirty/unmap sequence References: <4F6C2E9B.9010200@gmail.com> <4F6C31F7.2010804@jp.fujitsu.com> In-Reply-To: <4F6C31F7.2010804@jp.fujitsu.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" On 2012a1'03ae??23ae?JPY 16:19, KAMEZAWA Hiroyuki wrote: > (2012/03/23 17:04), bill4carson wrote: > >> Hi, all >> >> I'm playing with memory cgroup, I'm a bit confused why >> memory.usage in bytes is steadily increasing at 4K page pace >> after every mmap/dirty/unmap sequence. >> >> On linux-3.6.34.10/linux-3.3.0-rc5 >> A simple test case does following: >> >> a) mmap 128k memory in private anonymous way >> b) dirty all 128k to demand physical page >> c) print memory.usage_in_bytes<-- increased at 4K after every loop >> d) unmap previous 128 memory >> e) goto a) to repeat > > In Documentation/cgroup/memory.txt > == > 5.5 usage_in_bytes > > For efficiency, as other kernel components, memory cgroup uses some optimization > to avoid unnecessary cacheline false sharing. usage_in_bytes is affected by the > method and doesn't show 'exact' value of memory(and swap) usage, it's an fuzz > value for efficient access. (Of course, when necessary, it's synchronized.) > If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP) > value in memory.stat(see 5.2). > == > > In current implementation, memcg tries to charge resource in size of 32 pages. > So, if you get 32 pages and free 32pages, usage_in_bytes may not change. > This is affected by caches in other cpus and other flushing operations caused > by some workload in other cgroups. memcg's usage_in_bytes is not precise in > 128k degree. > Yes, I tried to mmap/dirty/unmap in 32 times, when the usage_in_bytes reached 128k, it rolls back to 4k again. So it doesn't hurt any more. I haven't found the code regarding to this behavior. > - How memory.stat changes ? > - What happens when you do test with 4M alloc/free ? > > Thanks, > -Kame > > > > > > > > > -- Love each day! --bill -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org