On Sun 28-02-16 19:19:11, Hugh Dickins wrote: > On Tue, 23 Feb 2016, Michal Hocko wrote: > > On Mon 22-02-16 17:36:07, David Rientjes wrote: > > > > > > Are we concerned about munlock_vma_pages_all() taking lock_page() and > > > perhaps stalling forever, the same way it would stall in exit_mmap() for > > > VM_LOCKED vmas, if another thread has locked the same page and is doing > > > an > > > allocation? > > > > This is a good question. I have checked for that particular case > > previously and managed to convinced myself that this is OK(ish). > > munlock_vma_pages_range locks only THP pages to prevent from the > > parallel split-up AFAICS. > > I think you're mistaken on that: there is also the lock_page() > on every page in Phase 2 of __munlock_pagevec().
Ohh, I have missed that one. Thanks for pointing it out! [...] > > Just for the reference this is what I came up with (just compile tested). > > I tried something similar internally (on an earlier kernel). Like > you I've set that work aside for now, there were quicker ways to fix > the issue at hand. But it does continue to offend me that munlock > demands all those page locks: so if you don't get back to it before me, > I shall eventually. > > I didn't understand why you complicated yours with the "enforce" > arg to munlock_vma_pages_range(): why not just trylock in all cases? Well, I have to confess that I am not really sure I understand all the consequences of the locking here. It has always been subtle and weird issues popping up from time to time. So I only wanted to have that change limitted to the oom_reaper. So I would really appreciate if somebody more knowledgeable had a look. We can drop the mlock patch for now. Thanks for looking into this, Hugh! -- Michal Hocko SUSE Labs
