From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 910B66B0006 for ; Fri, 2 Nov 2018 04:56:08 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id q10-v6so830938edd.20 for ; Fri, 02 Nov 2018 01:56:08 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id i15-v6si11335074edl.176.2018.11.02.01.56.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 02 Nov 2018 01:56:07 -0700 (PDT) Date: Fri, 2 Nov 2018 09:55:57 +0100 From: Michal Hocko Subject: Re: [PATCH RFC] mm: do not start node_reclaim for page order > MAX_ORDER Message-ID: <20181102081949.GQ23921@dhcp22.suse.cz> References: <154109387197.925352.10499549042420271600.stgit@buzz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <154109387197.925352.10499549042420271600.stgit@buzz> Sender: owner-linux-mm@kvack.org List-ID: To: Konstantin Khlebnikov Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org On Thu 01-11-18 20:37:52, Konstantin Khlebnikov wrote: > Page allocator has check in __alloc_pages_slowpath() but nowdays > there is earlier entry point into reclimer without such check: > get_page_from_freelist() -> node_reclaim(). Is the order check so expensive that it would be visible in the fast path? Spreading these MAX_ORDER checks sounds quite fragile to me. > Signed-off-by: Konstantin Khlebnikov > --- > mm/vmscan.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 62ac0c488624..52f672420f0b 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -4117,6 +4117,12 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order) > { > int ret; > > + /* > + * Do not scan if allocation will never succeed. > + */ > + if (order >= MAX_ORDER) > + return NODE_RECLAIM_NOSCAN; > + > /* > * Node reclaim reclaims unmapped file backed pages and > * slab pages if we are over the defined limits. > -- Michal Hocko SUSE Labs