From: Pavel Tatashin <[email protected]> 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/[email protected] 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 <[email protected]> Signed-off-by: Pavel Tatashin <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Reviewed-by: Daniel Jordan <[email protected]> Reviewed-by: David Hildenbrand <[email protected]> Acked-by: Michal Hocko <[email protected]> Acked-by: Vlastimil Babka <[email protected]> Cc: Dan Williams <[email protected]> Cc: James Morris <[email protected]> Cc: Kirill Tkhai <[email protected]> Cc: Sasha Levin <[email protected]> Cc: Yiqian Wei <[email protected]> Cc: <[email protected]> [4.17+] Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- include/linux/mmzone.h | 2 ++ mm/page_alloc.c | 19 +++++++------------ 2 files changed, 9 insertions(+), 12 deletions(-) --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -638,6 +638,8 @@ typedef struct pglist_data { /* * Must be held any time you expect node_start_pfn, node_present_pages * or node_spanned_pages 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 @@ -1586,6 +1586,13 @@ 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; @@ -1610,7 +1617,6 @@ static int __init deferred_init_memmap(v epfn = min_t(unsigned long, zone_end_pfn(zone), PFN_DOWN(epa)); deferred_free_pages(nid, zid, spfn, epfn); } - pgdat_resize_unlock(pgdat, &flags); /* Sanity check that the next zone really is unpopulated */ WARN_ON(++zid < MAX_NR_ZONES && populated_zone(++zone)); @@ -1657,17 +1663,6 @@ 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. */
