From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0F86CC433F5 for ; Wed, 16 Feb 2022 13:05:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233622AbiBPNGC (ORCPT ); Wed, 16 Feb 2022 08:06:02 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:47786 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231666AbiBPNGA (ORCPT ); Wed, 16 Feb 2022 08:06:00 -0500 Received: from outbound-smtp04.blacknight.com (outbound-smtp04.blacknight.com [81.17.249.35]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7A9A261214 for ; Wed, 16 Feb 2022 05:05:46 -0800 (PST) Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp04.blacknight.com (Postfix) with ESMTPS id 4E964BED69 for ; Wed, 16 Feb 2022 13:05:45 +0000 (GMT) Received: (qmail 28902 invoked from network); 16 Feb 2022 13:05:45 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.17.223]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 16 Feb 2022 13:05:44 -0000 Date: Wed, 16 Feb 2022 13:05:43 +0000 From: Mel Gorman To: Vlastimil Babka Cc: Andrew Morton , Aaron Lu , Dave Hansen , Michal Hocko , Jesper Dangaard Brouer , LKML , Linux-MM Subject: Re: [PATCH 2/5] mm/page_alloc: Track range of active PCP lists during bulk free Message-ID: <20220216130542.GT3366@techsingularity.net> References: <20220215145111.27082-1-mgorman@techsingularity.net> <20220215145111.27082-3-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 16, 2022 at 01:02:01PM +0100, Vlastimil Babka wrote: > On 2/15/22 15:51, Mel Gorman wrote: > > free_pcppages_bulk() frees pages in a round-robin fashion. Originally, > > this was dealing only with migratetypes but storing high-order pages > > means that there can be many more empty lists that are uselessly > > checked. Track the minimum and maximum active pindex to reduce the > > search space. > > > > Signed-off-by: Mel Gorman > > --- > > mm/page_alloc.c | 13 +++++++++++-- > > 1 file changed, 11 insertions(+), 2 deletions(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 08de32cfd9bb..c5110fdeb115 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1450,6 +1450,8 @@ static void free_pcppages_bulk(struct zone *zone, int count, > > struct per_cpu_pages *pcp) > > { > > int pindex = 0; > > + int min_pindex = 0; > > + int max_pindex = NR_PCP_LISTS - 1; > > int batch_free = 0; > > int nr_freed = 0; > > unsigned int order; > > @@ -1478,10 +1480,17 @@ static void free_pcppages_bulk(struct zone *zone, int count, > > if (++pindex == NR_PCP_LISTS) > > Hmm, so in the very first iteration at this point pindex is already 1. This > looks odd even before the patch, as order 0 MIGRATE_UNMOVABLE list is only > processed after all the higher orders? > Yes and this was the behaviour before and after. I don't recall why. It might have been to preserve UNMOVABLE pages but after the series is finished, the reasoning is weak. I'll add a specific check. > > pindex = 0; > > Also shouldn't this wrap-around check also use min_index/max_index instead > of NR_PCP_LISTS and 0? > Yes, it should and it's a rebasing error from an earlier prototype that I missed. I'll fix it. > > list = &pcp->lists[pindex]; > > - } while (list_empty(list)); > > + if (!list_empty(list)) > > + break; > > + > > + if (pindex == max_pindex) > > + max_pindex--; > > + if (pindex == min_pindex) > > So with pindex 1 and min_pindex == 0 this will not trigger until > (eventually) the first pindex wrap around, which seems suboptimal. But I can > see the later patches change things substantially anyway so it may be moot... > It could potentially be more optimal but at the cost of complexity which I wanted to avoid in this path as much as possible. Initialising min_pindex == pindex could result in an infinite loop if the lower lists need to be cleared. -- Mel Gorman SUSE Labs