On Wed, Apr 1, 2020 at 3:57 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > 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. This is what I wanted to do, but after studying deferred_grow_zone(), I do not see a simple way to solve this. It is one thing to fail an allocation, and it is another thing to have a corruption because of race. > 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> Thank you, Pasha > > 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
