From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id ACE5D28027D for ; Fri, 11 Nov 2016 05:30:42 -0500 (EST) Received: by mail-pf0-f197.google.com with SMTP id 17so9613367pfy.2 for ; Fri, 11 Nov 2016 02:30:42 -0800 (PST) Received: from mail-pf0-x231.google.com (mail-pf0-x231.google.com. [2607:f8b0:400e:c00::231]) by mx.google.com with ESMTPS id cs1si7960352pac.117.2016.11.11.02.30.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 11 Nov 2016 02:30:41 -0800 (PST) Received: by mail-pf0-x231.google.com with SMTP id d2so10225750pfd.0 for ; Fri, 11 Nov 2016 02:30:41 -0800 (PST) Date: Fri, 11 Nov 2016 02:30:39 -0800 (PST) From: David Rientjes Subject: Re: [patch] mm, slab: faster active and free stats In-Reply-To: <20161111055326.GA16336@js1304-P5Q-DELUXE> Message-ID: References: <20161108151727.b64035da825c69bced88b46d@linux-foundation.org> <20161111055326.GA16336@js1304-P5Q-DELUXE> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim Cc: Andrew Morton , Greg Thelen , Aruna Ramakrishna , Christoph Lameter , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Fri, 11 Nov 2016, Joonsoo Kim wrote: > Hello, David. > > Maintaining acitve/free_slab counters looks so complex. And, I think > that we don't need to maintain these counters for faster slabinfo. > Key point is to remove iterating n->slabs_partial list. > > We can calculate active slab/object by following equation as you did in > this patch. > > active_slab(n) = n->num_slab - the number of free_slab > active_object(n) = n->num_slab * cachep->num - n->free_objects > > To get the number of free_slab, we need to iterate n->slabs_free list > but I guess it would be small enough. > > If you don't like to iterate n->slabs_free list in slabinfo, just > maintaining the number of slabs_free would be enough. > Hi Joonsoo, It's a good point, although I don't think the patch has overly complex logic to keep track of slab state. We don't prefer to do any iteration in get_slabinfo() since users can read /proc/slabinfo constantly; it's better to just settle the stats when slab state changes instead of repeating an expensive operation over and over if someone is running slabtop(1) or /proc/slabinfo is scraped regularly for stats. That said, I imagine there are more clever ways to arrive at the same answer, and you bring up a good point about maintaining a n->num_slabs and n->free_slabs rather than n->active_slabs and n->free_slabs. I don't feel strongly about either approach, but I think some improvement, such as what this patch provides, is needed to prevent how expensive simply reading /proc/slabinfo can be. -- 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