From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753764AbaAICYi (ORCPT ); Wed, 8 Jan 2014 21:24:38 -0500 Received: from mail-yh0-f46.google.com ([209.85.213.46]:46373 "EHLO mail-yh0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752382AbaAICYg (ORCPT ); Wed, 8 Jan 2014 21:24:36 -0500 Date: Wed, 8 Jan 2014 18:24:33 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Dave Hansen cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cl@linux-foundation.org, akpm@linux-foundation.org, penberg@kernel.org Subject: Re: [PATCH] mm: slub: fix ALLOC_SLOWPATH stat In-Reply-To: <20140106204300.DE79BA86@viggo.jf.intel.com> Message-ID: References: <20140106204300.DE79BA86@viggo.jf.intel.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 6 Jan 2014, Dave Hansen wrote: > There used to be only one path out of __slab_alloc(), and > ALLOC_SLOWPATH got bumped in that exit path. Now there are two, > and a bunch of gotos. ALLOC_SLOWPATH can now get set more than once > during a single call to __slab_alloc() which is pretty bogus. > Here's the sequence: > > 1. Enter __slab_alloc(), fall through all the way to the > stat(s, ALLOC_SLOWPATH); > 2. hit 'if (!freelist)', and bump DEACTIVATE_BYPASS, jump to > new_slab (goto #1) > 3. Hit 'if (c->partial)', bump CPU_PARTIAL_ALLOC, goto redo > (goto #2) > 4. Fall through in the same path we did before all the way to > stat(s, ALLOC_SLOWPATH) > 5. bump ALLOC_REFILL stat, then return > > Doing this is obviously bogus. It keeps us from being able to > accurately compare ALLOC_SLOWPATH vs. ALLOC_FASTPATH. It also > means that the total number of allocs always exceeds the total > number of frees. > > This patch moves stat(s, ALLOC_SLOWPATH) to be called from the > same place that __slab_alloc() is. This makes it much less > likely that ALLOC_SLOWPATH will get botched again in the > spaghetti-code inside __slab_alloc(). > > Signed-off-by: Dave Hansen Acked-by: David Rientjes