linux-kernel - [PATCH 5.7 269/376] mm: initialize deferred pages with interrupts enabled

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Date:   Fri, 19 Jun 2020 16:33:07 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Shile Zhang <shile.zhang@...ux.alibaba.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        James Morris <jmorris@...ei.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Sasha Levin <sashal@...nel.org>, Yiqian Wei <yiwei@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.7 269/376] mm: initialize deferred pages with interrupts enabled

From: Pavel Tatashin <pasha.tatashin@...een.com>

commit 3d060856adfc59afb9d029c233141334cfaba418 upstream.

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@...ux.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

Fixes: 3a2d7fa8a3d5 ("mm: disable interrupts while initializing deferred pages")
Reported-by: Shile Zhang <shile.zhang@...ux.alibaba.com>
Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Reviewed-by: Daniel Jordan <daniel.m.jordan@...cle.com>
Reviewed-by: David Hildenbrand <david@...hat.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: James Morris <jmorris@...ei.org>
Cc: Kirill Tkhai <ktkhai@...tuozzo.com>
Cc: Sasha Levin <sashal@...nel.org>
Cc: Yiqian Wei <yiwei@...hat.com>
Cc: <stable@...r.kernel.org>	[4.17+]
Link: http://lkml.kernel.org/r/20200403140952.17177-3-pasha.tatashin@soleen.com
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 include/linux/mmzone.h |    2 ++
 mm/page_alloc.c        |   20 +++++++-------------
 2 files changed, 9 insertions(+), 13 deletions(-)

--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -678,6 +678,8 @@ 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
+++ b/mm/page_alloc.c
@@ -1845,6 +1845,13 @@ 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;
@@ -1865,8 +1872,6 @@ static int __init deferred_init_memmap(v
 	while (spfn < epfn)
 		nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
 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));
 
@@ -1909,17 +1914,6 @@ 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;
-	}
-
-	/*
 	 * If someone grew this zone while we were waiting for spinlock, return
 	 * true, as there might be enough pages already.
 	 */