Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753082AbdHGLkr (ORCPT ); Mon, 7 Aug 2017 07:40:47 -0400 Received: from mx2.suse.de ([195.135.220.15]:57573 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752835AbdHGLkq (ORCPT ); Mon, 7 Aug 2017 07:40:46 -0400 Date: Mon, 7 Aug 2017 13:40:43 +0200 From: Michal Hocko To: Wei Yang Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Tejun Heo Subject: Re: [PATCH] mm/vmalloc: reduce half comparison during pcpu_get_vm_areas() Message-ID: <20170807114043.GG32434@dhcp22.suse.cz> References: <20170803063822.48702-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170803063822.48702-1-richard.weiyang@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1959 Lines: 55 [CC Tejun] On Thu 03-08-17 14:38:22, Wei Yang wrote: > In pcpu_get_vm_areas(), it checks each range is not overlapped. To make > sure it is, only (N^2)/2 comparison is necessary, while current code does > N^2 times. By starting from the next range, it achieves the goal and the > continue could be removed. > > At the mean time, other two work in this patch: > * the overlap check of two ranges could be done with one clause > * one typo in comment is fixed. > > Signed-off-by: Wei Yang > --- > mm/vmalloc.c | 10 +++------- > 1 file changed, 3 insertions(+), 7 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 8087451cb332..f33c8350fd83 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -2457,7 +2457,7 @@ static unsigned long pvm_determine_end(struct vmap_area **pnext, > * matching slot. While scanning, if any of the areas overlaps with > * existing vmap_area, the base address is pulled down to fit the > * area. Scanning is repeated till all the areas fit and then all > - * necessary data structres are inserted and the result is returned. > + * necessary data structures are inserted and the result is returned. > */ > struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets, > const size_t *sizes, int nr_vms, > @@ -2485,15 +2485,11 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets, > if (start > offsets[last_area]) > last_area = area; > > - for (area2 = 0; area2 < nr_vms; area2++) { > + for (area2 = area + 1; area2 < nr_vms; area2++) { > unsigned long start2 = offsets[area2]; > unsigned long end2 = start2 + sizes[area2]; > > - if (area2 == area) > - continue; > - > - BUG_ON(start2 >= start && start2 < end); > - BUG_ON(end2 <= end && end2 > start); > + BUG_ON(start2 < end && start < end2); > } > } > last_end = offsets[last_area] + sizes[last_area]; > -- > 2.11.0 > -- Michal Hocko SUSE Labs