From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 050/131] mm: initialize deferred pages with interrupts enabled Date: Wed, 03 Jun 2020 15:59:24 -0700 Message-ID: <20200603225924.kDWBwWWfU%akpm@linux-foundation.org> References: <20200603155549.e041363450869eaae4c7f05b@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:41482 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725821AbgFCW7Z (ORCPT ); Wed, 3 Jun 2020 18:59:25 -0400 In-Reply-To: <20200603155549.e041363450869eaae4c7f05b@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, dan.j.williams@intel.com, daniel.m.jordan@oracle.com, david@redhat.com, jmorris@namei.org, ktkhai@virtuozzo.com, linux-mm@kvack.org, mhocko@suse.com, mm-commits@vger.kernel.org, pasha.tatashin@soleen.com, sashal@kernel.org, shile.zhang@linux.alibaba.com, stable@vger.kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz, yiwei@redhat.com From: Pavel Tatashin Subject: mm: initialize deferred pages with interrupts enabled 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). Let's 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 Link: http://lkml.kernel.org/r/20200403140952.17177-3-pasha.tatashin@soleen.com Fixes: 3a2d7fa8a3d5 ("mm: disable interrupts while initializing deferred pages") Reported-by: Shile Zhang Signed-off-by: Pavel Tatashin Reviewed-by: Daniel Jordan Acked-by: Michal Hocko Acked-by: Vlastimil Babka Reviewed-by: David Hildenbrand Cc: Dan Williams Cc: James Morris Cc: Kirill Tkhai Cc: Sasha Levin Cc: Yiqian Wei Cc: [4.17+] Signed-off-by: Andrew Morton --- include/linux/mmzone.h | 2 ++ mm/page_alloc.c | 20 +++++++------------- 2 files changed, 9 insertions(+), 13 deletions(-) --- a/include/linux/mmzone.h~mm-initialize-deferred-pages-with-interrupts-enabled +++ a/include/linux/mmzone.h @@ -680,6 +680,8 @@ 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 --- a/mm/page_alloc.c~mm-initialize-deferred-pages-with-interrupts-enabled +++ a/mm/page_alloc.c @@ -1844,6 +1844,13 @@ static int __init deferred_init_memmap(v 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; @@ -1866,8 +1873,6 @@ static int __init deferred_init_memmap(v touch_nmi_watchdog(); } 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)); @@ -1910,17 +1915,6 @@ deferred_grow_zone(struct zone *zone, un 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; - }