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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 0CFB4C2BA15 for ; Thu, 2 Apr 2020 12:09:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E1F7E20757 for ; Thu, 2 Apr 2020 12:09:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388217AbgDBMJ1 (ORCPT ); Thu, 2 Apr 2020 08:09:27 -0400 Received: from mx2.suse.de ([195.135.220.15]:39218 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387958AbgDBMJ1 (ORCPT ); Thu, 2 Apr 2020 08:09:27 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 85F2CAA55; Thu, 2 Apr 2020 12:09:24 +0000 (UTC) Subject: Re: [PATCH v2 2/2] mm: initialize deferred pages with interrupts enabled To: Pavel Tatashin , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mhocko@suse.com, linux-mm@kvack.org, dan.j.williams@intel.com, shile.zhang@linux.alibaba.com, daniel.m.jordan@oracle.com, ktkhai@virtuozzo.com, david@redhat.com, jmorris@namei.org, sashal@kernel.org References: <20200401225723.14164-1-pasha.tatashin@soleen.com> <20200401225723.14164-3-pasha.tatashin@soleen.com> From: Vlastimil Babka Message-ID: <8a2fbe6b-c861-9d47-9f02-72d476265359@suse.cz> Date: Thu, 2 Apr 2020 14:09:24 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200401225723.14164-3-pasha.tatashin@soleen.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/2/20 12:57 AM, Pavel Tatashin wrote: > Initializing struct pages is a long task and keeping interrupts disabled > for the duration of this operation introduces a number of problems. > > 1. jiffies are not updated for long period of time, and thus incorrect time > is reported. See proposed solution and discussion here: > lkml/20200311123848.118638-1-shile.zhang@linux.alibaba.com > 2. It prevents farther improving deferred page initialization by allowing > intra-node multi-threading. > > We are keeping interrupts disabled to solve a rather theoretical problem > that was never observed in real world (See 3a2d7fa8a3d5). > > Lets keep interrupts enabled. In case we ever encounter a scenario where > an interrupt thread wants to allocate large amount of memory this early in > boot we can deal with that by growing zone (see deferred_grow_zone()) by > the needed amount before starting deferred_init_memmap() threads. > > Before: > [ 1.232459] node 0 initialised, 12058412 pages in 1ms > > After: > [ 1.632580] node 0 initialised, 12051227 pages in 436ms > > Fixes: 3a2d7fa8a3d5 ("mm: disable interrupts while initializing deferred pages") > Cc: stable@vger.kernel.org # 4.17+ TBH I don't remember my concern anymore. Reading my mail now [1] it seems I was thinking the problem could happen not just in interrupt context, but with other kthreads as well. Anyway I agree with the approach of waiting for actual issues being reported and then eventually pre-growing more. Acked-by: Vlastimil Babka [1] https://lore.kernel.org/linux-mm/33e3a3ff-0318-1a07-3c57-6be638046c87@suse.cz/ > Reported-by: Shile Zhang > Signed-off-by: Pavel Tatashin > Reviewed-by: Daniel Jordan > Acked-by: Michal Hocko > --- > include/linux/mmzone.h | 2 ++ > mm/page_alloc.c | 22 ++++++++-------------- > 2 files changed, 10 insertions(+), 14 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 462f6873905a..c5bdf55da034 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -721,6 +721,8 @@ typedef struct pglist_data { > /* > * Must be held any time you expect node_start_pfn, > * node_present_pages, node_spanned_pages or nr_zones to stay constant. > + * Also synchronizes pgdat->first_deferred_pfn during deferred page > + * init. > * > * pgdat_resize_lock() and pgdat_resize_unlock() are provided to > * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index e8ff6a176164..68669d3a5a66 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1790,6 +1790,13 @@ static int __init deferred_init_memmap(void *data) > BUG_ON(pgdat->first_deferred_pfn > pgdat_end_pfn(pgdat)); > pgdat->first_deferred_pfn = ULONG_MAX; > > + /* > + * Once we unlock here, the zone cannot be grown anymore, thus if an > + * interrupt thread must allocate this early in boot, zone must be > + * pre-grown prior to start of deferred page initialization. > + */ > + pgdat_resize_unlock(pgdat, &flags); > + > /* Only the highest zone is deferred so find it */ > for (zid = 0; zid < MAX_NR_ZONES; zid++) { > zone = pgdat->node_zones + zid; > @@ -1809,11 +1816,9 @@ static int __init deferred_init_memmap(void *data) > */ > while (spfn < epfn) { > nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn); > - touch_nmi_watchdog(); > + cond_resched(); > } > zone_empty: > - pgdat_resize_unlock(pgdat, &flags); > - > /* Sanity check that the next zone really is unpopulated */ > WARN_ON(++zid < MAX_NR_ZONES && populated_zone(++zone)); > > @@ -1855,17 +1860,6 @@ deferred_grow_zone(struct zone *zone, unsigned int order) > > pgdat_resize_lock(pgdat, &flags); > > - /* > - * If deferred pages have been initialized while we were waiting for > - * the lock, return true, as the zone was grown. The caller will retry > - * this zone. We won't return to this function since the caller also > - * has this static branch. > - */ > - if (!static_branch_unlikely(&deferred_pages)) { > - pgdat_resize_unlock(pgdat, &flags); > - return true; > - } > - > /* > * If someone grew this zone while we were waiting for spinlock, return > * true, as there might be enough pages already. >