From: Pavel Tatashin pasha.tatashin@soleen.com 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 shile.zhang@linux.alibaba.com Signed-off-by: Pavel Tatashin pasha.tatashin@soleen.com Reviewed-by: Daniel Jordan daniel.m.jordan@oracle.com Acked-by: Michal Hocko mhocko@suse.com Acked-by: Vlastimil Babka vbabka@suse.cz Reviewed-by: David Hildenbrand david@redhat.com 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+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
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; - } - - /* * If someone grew this zone while we were waiting for spinlock, return * true, as there might be enough pages already. */ _