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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 DE3EFC433E2 for ; Thu, 17 Sep 2020 16:25:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A2400206E6 for ; Thu, 17 Sep 2020 16:25:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728512AbgIQQZj (ORCPT ); Thu, 17 Sep 2020 12:25:39 -0400 Received: from mx2.suse.de ([195.135.220.15]:33002 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728418AbgIQQXr (ORCPT ); Thu, 17 Sep 2020 12:23:47 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id AD7A1B2C6; Thu, 17 Sep 2020 16:06:08 +0000 (UTC) Subject: Re: [RFC 1/5] mm, page_alloc: clean up pageset high and batch update To: Oscar Salvador Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko , Pavel Tatashin , David Hildenbrand , Joonsoo Kim References: <20200907163628.26495-1-vbabka@suse.cz> <20200907163628.26495-2-vbabka@suse.cz> <20200910083116.GA2285@linux> From: Vlastimil Babka Message-ID: <78f43f31-4388-923f-83aa-dc9831de6e18@suse.cz> Date: Thu, 17 Sep 2020 18:05:33 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200910083116.GA2285@linux> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/10/20 10:31 AM, Oscar Salvador wrote: > On Mon, Sep 07, 2020 at 06:36:24PM +0200, Vlastimil Babka wrote: > >> -/* >> - * pageset_set_high() sets the high water mark for hot per_cpu_pagelist >> - * to the value high for the pageset p. >> - */ >> -static void pageset_set_high(struct per_cpu_pageset *p, >> - unsigned long high) >> -{ >> - unsigned long batch = max(1UL, high / 4); >> - if ((high / 4) > (PAGE_SHIFT * 8)) >> - batch = PAGE_SHIFT * 8; >> - >> - pageset_update(&p->pcp, high, batch); >> + pageset_update(&p->pcp, 0, 1); >> } > > Could we restore the comment we had in pageset_set_high, and maybe > update it to match this new function? I think it would be useful. Same as David, I didn't find the comment useful at all. But I can try writing a better one instead. >> >> static void pageset_set_high_and_batch(struct zone *zone, >> - struct per_cpu_pageset *pcp) >> + struct per_cpu_pageset *p) >> { >> - if (percpu_pagelist_fraction) >> - pageset_set_high(pcp, >> - (zone_managed_pages(zone) / >> - percpu_pagelist_fraction)); >> - else >> - pageset_set_batch(pcp, zone_batchsize(zone)); >> + unsigned long new_high; >> + unsigned long new_batch; >> + int fraction = READ_ONCE(percpu_pagelist_fraction); > > Why the READ_ONCE? In case there is a parallel update so things to get > messed up? Yeah, I think online of a new zone can race with sysctl update to percpu_pagelist_fraction, because online doesn't take pcp_batch_high_lock... until patch 5. But you're right this should be separate. > as I said, I'd appreciate a comment in pageset_set_high_and_batch to be > restored and updated, otherwise: > > Reviewed-by: Oscar Salvador Thanks! > Thanks >