From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id C9D2A6B0008 for ; Tue, 27 Mar 2018 06:58:24 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id g13so11353646wrh.23 for ; Tue, 27 Mar 2018 03:58:24 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id a6si710901wri.535.2018.03.27.03.58.23 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 27 Mar 2018 03:58:23 -0700 (PDT) Date: Tue, 27 Mar 2018 12:58:21 +0200 From: Michal Hocko Subject: Re: [PATCH] mm/page_alloc: break on the first hit of mem range Message-ID: <20180327105821.GF5652@dhcp22.suse.cz> References: <20180327035707.84113-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180327035707.84113-1-richard.weiyang@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Wei Yang Cc: akpm@linux-foundation.org, tj@kernel.org, linux-mm@kvack.org On Tue 27-03-18 11:57:07, Wei Yang wrote: > find_min_pfn_for_node() iterate on pfn range to find the minimum pfn for a > node. The memblock_region in memblock_type are already ordered, which means > the first hit in iteration is the minimum pfn. I haven't looked at the code yet but the changelog should contain the motivation why it exists. It seems like this is an optimization. If so, what is the impact? > This patch returns the fist hit instead of iterating the whole regions. > > Signed-off-by: Wei Yang > --- > mm/page_alloc.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 635d7dd29d7f..a65de1ec4b91 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -6365,14 +6365,14 @@ unsigned long __init node_map_pfn_alignment(void) > /* Find the lowest pfn for a node */ > static unsigned long __init find_min_pfn_for_node(int nid) > { > - unsigned long min_pfn = ULONG_MAX; > - unsigned long start_pfn; > + unsigned long min_pfn; > int i; > > - for_each_mem_pfn_range(i, nid, &start_pfn, NULL, NULL) > - min_pfn = min(min_pfn, start_pfn); > + for_each_mem_pfn_range(i, nid, &min_pfn, NULL, NULL) { > + break; > + } > > - if (min_pfn == ULONG_MAX) { > + if (i == -1) { > pr_warn("Could not find start_pfn for node %d\n", nid); > return 0; > } > -- > 2.15.1 > -- Michal Hocko SUSE Labs