On Mon 29-07-19 11:49:52, Johannes Weiner wrote: > On Sun, Jul 28, 2019 at 03:29:38PM +0300, Konstantin Khlebnikov wrote: > > --- a/mm/gup.c > > +++ b/mm/gup.c > > @@ -847,8 +847,11 @@ static long __get_user_pages(struct task_struct *tsk, > > struct mm_struct *mm, > > ret = -ERESTARTSYS; > > goto out; > > } > > - cond_resched(); > > > > + /* Reclaim memory over high limit before stocking too much */ > > + mem_cgroup_handle_over_high(true); > > I'd rather this remained part of the try_charge() call. The code > comment in try_charge says this: > > * We can perform reclaim here if __GFP_RECLAIM but let's > * always punt for simplicity and so that GFP_KERNEL can > * consistently be used during reclaim. > > The simplicity argument doesn't hold true anymore once we have to add > manual calls into allocation sites. We should instead fix try_charge() > to do synchronous reclaim for __GFP_RECLAIM and only punt to userspace > return when actually needed.
Agreed. If we want to do direct reclaim on the high limit breach then it should go into try_charge same way we do hard limit reclaim there. I am not yet sure about how/whether to scale the excess. The only reason to move reclaim to return-to-userspace path was GFP_NOWAIT charges. As you say, maybe we should start by always performing the reclaim for sleepable contexts first and only defer for non-sleeping requests. -- Michal Hocko SUSE Labs
