Commit 3d060856 authored Jun 03, 2020 by Pavel Tatashin Committed by Linus Torvalds Jun 03, 2020

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 3a2d7fa8).

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: 3a2d7fa8 ("mm: disable interrupts while initializing deferred pages")
Reported-by: Shile Zhang <shile.zhang@linux.alibaba.com>
Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: James Morris <jmorris@namei.org>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Yiqian Wei <yiwei@redhat.com>
Cc: <stable@vger.kernel.org>	[4.17+]
Link: http://lkml.kernel.org/r/20200403140952.17177-3-pasha.tatashin@soleen.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 117003c3

include/linux/mmzone.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -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

mm/page_alloc.c

+7 −13

Original line number	Diff line number	Diff line
		@@ -1844,6 +1844,13 @@ 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;
		@@ -1866,8 +1873,6 @@ static int __init deferred_init_memmap(void *data)
		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));

		@@ -1909,17 +1914,6 @@ 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.

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