Re: [PATCH] mm/hugetlb: Warn the user when issues arise on boot due to hugepages

[Michal Hocko <mhocko@suse.com>]

On Tue 13-06-17 11:25:02, Liam R. Howlett wrote:
> * Michal Hocko <mhocko@suse.com> [170613 01:42]:
> > On Mon 12-06-17 21:35:17, Liam R. Howlett wrote:
> > [...]
> > > Understood.  Again, I appreciate all the time you have taken on my
> > > patch and explaining your points.  I will look at this again as you
> > > have suggested.
> > 
> > One way to go forward might be to check the size of the per node pool
> > and warn if it grows over a certain threshold of the available memory
> > on that node. I do not have a good idea what would be that threshold,
> > though. It will certainly depend on workloads. I can also imagine that
> > somebody might want to dedicate the full numa node for hugetlb pages
> > and still be OK so take this suggestion with some reserve. It is hard
> > to protect against misconfigurations in general but maybe you will find
> > some way here.
> 
> I thought about an upper threshold of memory and discussed it
> internally, but came to the same conclusion; it may be desired and
> there's no safe bet beyond warning if the user requests over 100% of the
> memory.  In the case of requesting over 100% of the memory, we could
> warn the user and specify what was allocated.  Would it be reasonable to
> warn on both boot and through sysfs of such requests?  I'm concerned
> that this is yet another too-targeted approach.

No, I think 100% is just too targeted. As I've said already said, a good
enough treshold might be hard to get right but filling up more than 90%
of memory with hugetlb pages will just bite you unless you know what you
are doing. And if so you can safely ignore such a warning...
-- 
Michal Hocko
SUSE Labs

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>