On Wed 01-04-20 16:27:33, Pavel Tatashin wrote: > 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. Let's discuss deferred_grow_zone after this all settles down. I still have to study it because I wasn't aware that this is actually a page allocator path relying on the resize lock. My recollection was that the resize lock is only about memory hotplug. Your patches flew by and I didn't have time to review them back then. So I have to admit I have seen the resize lock too simple. -- Michal Hocko SUSE Labs
