From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 4 Nov 2005 00:02:12 -0800 From: Andrew Morton Subject: Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19 Message-Id: <20051104000212.2e0e92bd.akpm@osdl.org> In-Reply-To: <20051103234530.5fcb2825.pj@sgi.com> References: <200511021747.45599.rob@landley.net> <43699573.4070301@yahoo.com.au> <200511030007.34285.rob@landley.net> <20051103163555.GA4174@ccure.user-mode-linux.org> <1131035000.24503.135.camel@localhost.localdomain> <20051103205202.4417acf4.akpm@osdl.org> <20051103213538.7f037b3a.pj@sgi.com> <20051103214807.68a3063c.akpm@osdl.org> <20051103224239.7a9aee29.pj@sgi.com> <20051103231019.488127a6.akpm@osdl.org> <20051103234530.5fcb2825.pj@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Paul Jackson Cc: bron@bronze.corp.sgi.com, pbadari@gmail.com, jdike@addtoit.com, rob@landley.net, nickpiggin@yahoo.com.au, gh@us.ibm.com, mingo@elte.hu, kamezawa.hiroyu@jp.fujitsu.com, haveblue@us.ibm.com, mel@csn.ul.ie, mbligh@mbligh.org, kravetz@us.ibm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, lhms-devel@lists.sourceforge.net List-ID: Paul Jackson wrote: > > A per-task stat requires walking the tasklist, to build a list of the > tasks to query. Nope, just task->mm->whatever. > A raw counter requires repeated polling to determine the recent rate of > activity. True. > The filtered per-cpuset rate avoids any need to repeatedly access > global resources such as the tasklist, and minimizes the total cpu > cycles required to get the interesting stat. > Well no. Because the filtered-whatsit takes two spinlocks and does a bunch of arith for each and every task, each time it calls try_to_free_pages(). The frequency of that could be very high indeed, even when nobody is interested in the metric which is being maintained(!). And I'd suggest that only a minority of workloads would be interested in this metric? ergo, polling the thing once per five seconds in those situations where we actually want to poll the thing may well be cheaper, in global terms? -- 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/ . Don't email: email@kvack.org