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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 86724C433E1 for ; Tue, 25 Aug 2020 05:10:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 652B82071E for ; Tue, 25 Aug 2020 05:10:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598332255; bh=Tm5TGS9QxUQnZMSBd7cObay8VgPGZsJUas2eWOf9csE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=rnCaNRyJWeKFuOidqbZBYzbzhD1ZL+UBqnQhGaypoCqniY2KE5uEXkotDMfr6d/rc z2fDlGQVHabaU3uvjS8JG26YuUBdcsDqZx43tYdTl5cOjxvt4/rbSz8mn7RuxC3/UX PEbcFemB06g+p0Tex4H3ObMCYC78SakzOWN5wf9M= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728109AbgHYFKv (ORCPT ); Tue, 25 Aug 2020 01:10:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:55148 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725781AbgHYFKv (ORCPT ); Tue, 25 Aug 2020 01:10:51 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (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 27D782071E; Tue, 25 Aug 2020 05:10:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598332250; bh=Tm5TGS9QxUQnZMSBd7cObay8VgPGZsJUas2eWOf9csE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=T43Wjah61jO7E4dy/ROpCXV6YaMsYbfXW65GEfmoSfuVTQHHiONBQPnQ9AHvCiKKZ FnENnMAAPPpMAXEuoT5HpmlSTg1/Sfix7DgfKuLLIASWuAlEajxtod+WhD9StoKoVB kbV5AUYwDsPcWT8q18WH9VdGEL5wj/mrD3m6lKcg= Date: Mon, 24 Aug 2020 22:10:49 -0700 From: Andrew Morton To: js1304@gmail.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko , Vlastimil Babka , "Aneesh Kumar K . V" , kernel-team@lge.com, Joonsoo Kim Subject: Re: [PATCH for v5.9] mm/page_alloc: handle a missing case for memalloc_nocma_{save/restore} APIs Message-Id: <20200824221049.edb3c540bbfc859a6806600d@linux-foundation.org> In-Reply-To: <1598331582-19923-1-git-send-email-iamjoonsoo.kim@lge.com> References: <1598331582-19923-1-git-send-email-iamjoonsoo.kim@lge.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 25 Aug 2020 13:59:42 +0900 js1304@gmail.com wrote: > From: Joonsoo Kim > > memalloc_nocma_{save/restore} APIs can be used to skip page allocation > on CMA area, but, there is a missing case and the page on CMA area could > be allocated even if APIs are used. This patch handles this case to fix > the potential issue. > > Missing case is an allocation from the pcplist. MIGRATE_MOVABLE pcplist > could have the pages on CMA area so we need to skip it if ALLOC_CMA isn't > specified. > > This patch implements this behaviour by checking allocated page from > the pcplist rather than skipping an allocation from the pcplist entirely. > Skipping the pcplist entirely would result in a mismatch between watermark > check and actual page allocation. And, it requires to break current code > layering that order-0 page is always handled by the pcplist. I'd prefer > to avoid it so this patch uses different way to skip CMA page allocation > from the pcplist. > > ... > > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3341,6 +3341,22 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone, > pcp = &this_cpu_ptr(zone->pageset)->pcp; > list = &pcp->lists[migratetype]; > page = __rmqueue_pcplist(zone, migratetype, alloc_flags, pcp, list); > +#ifdef CONFIG_CMA > + if (page) { > + int mt = get_pcppage_migratetype(page); > + > + /* > + * pcp could have the pages on CMA area and we need to skip it > + * when !ALLOC_CMA. Free all pcplist and retry allocation. > + */ > + if (is_migrate_cma(mt) && !(alloc_flags & ALLOC_CMA)) { > + list_add(&page->lru, &pcp->lists[migratetype]); > + pcp->count++; > + free_pcppages_bulk(zone, pcp->count, pcp); > + page = __rmqueue_pcplist(zone, migratetype, alloc_flags, pcp, list); > + } > + } > +#endif > if (page) { > __count_zid_vm_events(PGALLOC, page_zonenum(page), 1); > zone_statistics(preferred_zone, zone); That's a bunch more code on a very hot path to serve an obscure feature which has a single obscure callsite. Can we instead put the burden on that callsite rather than upon everyone? For (dumb) example, teach __gup_longterm_locked() to put the page back if it's CMA and go get another one?