On Wed 01-04-20 15:32:38, Pavel Tatashin wrote: > 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@xxxxxxxxxxxxxxxxx http://lkml.kernel.org/r/20200311123848.118638-1-shile.zhang@xxxxxxxxxxxxxxxxx > 2. It prevents farther improving deferred page initialization by allowing > inter-node multi-threading. > > We are keeping interrupts disabled to solve a rather theoretical problem > that was never observed in real world (See 3a2d7fa8a3d5). > > Lets 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") > Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> I would much rather see pgdat_resize_lock completely out of both the allocator and deferred init path altogether but this can be done in a separate patch. This one looks slightly safer for stable backports. To be completely honest I would love to see the resize lock go away completely. That might need a deeper thought but I believe it is something that has never been done properly. Acked-by: Michal Hocko <mhocko@xxxxxxxx> Thanks! > --- > mm/page_alloc.c | 21 +++++++-------------- > 1 file changed, 7 insertions(+), 14 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3c4eb750a199..4498a13b372d 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1792,6 +1792,13 @@ 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; > @@ -1812,8 +1819,6 @@ static int __init deferred_init_memmap(void *data) > 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)); > > @@ -1854,18 +1859,6 @@ deferred_grow_zone(struct zone *zone, unsigned int order) > return false; > > 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. > -- > 2.17.1 > -- Michal Hocko SUSE Labs
