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 X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D26C9C433DF for ; Fri, 14 Aug 2020 23:27:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A9C5120774 for ; Fri, 14 Aug 2020 23:27:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597447665; bh=GPjCjOBy4/MES/6xwTtupSAhE2pRWrieYpnW2v2mWIY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=q/Bcvi1EuYL5WihWbXUSwHgsVuD5KoMsgOIW/SfX/WqIBY3PkZ1UjD1pfgwOHcFm0 8OWzeCQiaa+ww9FJREvyXxd44pr8wtgEYxip2UiuTmAEtQ0jV/Upz3tEOFyVw63XwJ 7sBnsf93aUaPoaIaautgzMojzCfo1UAhVlUmByBk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726897AbgHNX1p (ORCPT ); Fri, 14 Aug 2020 19:27:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:43346 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726795AbgHNX1p (ORCPT ); Fri, 14 Aug 2020 19:27:45 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4EFC820768; Fri, 14 Aug 2020 23:27:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597447664; bh=GPjCjOBy4/MES/6xwTtupSAhE2pRWrieYpnW2v2mWIY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=HvU9bzcZLYnzdJR10tU7jmktoTLxECTfl1592MQ0btRmVKPDyYxeX+5c/Cau6KbMf +7RSeUurYeeS5/b1PkHxL7kD90k3yUvHMgn5ZBiyLKgXWuhT+m7qkl9DcJh3CVaQnW R/fOqJkGx/heLGwwJuNemyzyo/fzO0U7xo9S0Ej8= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 2CD063522B27; Fri, 14 Aug 2020 16:27:44 -0700 (PDT) Date: Fri, 14 Aug 2020 16:27:44 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Thomas Gleixner , Michal Hocko , Uladzislau Rezki , LKML , RCU , linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Matthew Wilcox , "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag Message-ID: <20200814232744.GU4295@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200813220619.GA2674@hirez.programming.kicks-ass.net> <875z9m3xo7.fsf@nanos.tec.linutronix.de> <20200814083037.GD3982@worktop.programming.kicks-ass.net> <20200814141425.GM4295@paulmck-ThinkPad-P72> <20200814161106.GA13853@paulmck-ThinkPad-P72> <20200814174924.GI3982@worktop.programming.kicks-ass.net> <20200814180224.GQ4295@paulmck-ThinkPad-P72> <875z9lkoo4.fsf@nanos.tec.linutronix.de> <20200814204140.GT4295@paulmck-ThinkPad-P72> <20200814215206.GL3982@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200814215206.GL3982@worktop.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Fri, Aug 14, 2020 at 11:52:06PM +0200, Peter Zijlstra wrote: > On Fri, Aug 14, 2020 at 01:41:40PM -0700, Paul E. McKenney wrote: > > > And that enforces the GFP_NOLOCK allocation mode or some other solution > > > unless you make a new rule that calling call_rcu() is forbidden while > > > holding zone lock or any other lock which might be nested inside the > > > GFP_NOWAIT zone::lock held region. > > > > Again, you are correct. Maybe the forecasted weekend heat will cause > > my brain to hallucinate a better solution, but in the meantime, the > > GFP_NOLOCK approach looks good from this end. > > So I hate __GFP_NO_LOCKS for a whole number of reasons: > > - it should be called __GFP_LOCKLESS if anything > - it sprinkles a bunch of ugly branches around the allocator fast path > - it only works for order==0 > > Combined I really odn't think this should be a GFP flag. How about a > special purpose allocation function, something like so.. This looks entirely reasonable to me! Thanx, Paul > --- > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 901a21f61d68..cdec9c99fba7 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4875,6 +4875,47 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid, > } > EXPORT_SYMBOL(__alloc_pages_nodemask); > > +struct page *__rmqueue_lockless(struct zone *zone, struct per_cpu_pages *pcp) > +{ > + struct list_head *list; > + struct page *page; > + int migratetype; > + > + for (migratetype = 0; migratetype < MIGRATE_PCPTYPES; migratetype++) { > + list = &pcp->list[migratetype]; > + page = list_first_entry_or_null(list, struct page, lru); > + if (page && check_new_pcp(page)) { > + list_del(&page->lru); > + pcp->count--; > + return page; > + } > + } > + > + return NULL; > +} > + > +struct page *__alloc_page_lockless(void) > +{ > + struct zonelist *zonelist = node_zonelist(numa_node_id(), GFP_KERNEL); > + struct per_cpu_pages *pcp; > + struct page *page = NULL; > + unsigned long flags; > + struct zoneref *z; > + struct zone *zone; > + > + for_each_zone_zonelist(zone, z, zonelist, ZONE_NORMAL) { > + local_irq_save(flags); > + pcp = &this_cpu_ptr(zone->pageset)->pcp; > + page = __rmqueue_lockless(zone, pcp); > + local_irq_restore(flags); > + > + if (page) > + break; > + } > + > + return page; > +} > + > /* > * Common helper functions. Never use with __GFP_HIGHMEM because the returned > * address cannot represent highmem pages. Use alloc_pages and then kmap if