Re: [RFC] mm: show message when updating min_free_kbytes in thp

David Rientjes
2014-01-15T00:53:03Z

On Tue, 14 Jan 2014, Andrew Morton wrote:

> I've been waiting 10+ years for us to decide to delete that warning due
> to the false positives. Hasn't happened yet, and the warning does
> find bugs/issues/misconfigurations/etc.
>

I've found memory leaks from the meminfo that is emitted as part of page
allocation failure warnings, that seems to be the only helpful part.
Unfortunately, they typically emit ~80 lines to the kernel log and become
quite verbose in succession. If you have a lot of nodes, it just becomes
longer.

I think we want to consider alternative values for the ratelimiter, in
this case nopage_rs that Dave added. Dave?

> > Would it be overkill to save the kernel default both with and without thp
> > and then doing a WARN_ON_ONCE() if a user-written value is ever less?
>
> Well, min_free_kbytes is a userspace thing, not a kernel thing - maybe
> THP shouldn't be dinking with it. What effect is THP trying to achieve
> and can we achieve it by other/better means?
>

It moved the preferred "hugeadm --set-recommended-min_free_kbytes"
behavior into the kernel that gave better results (due to lower occurrence
of fragmentation) for thp hosts. Previously, people were using hugeadm
in initscripts and then it became the default kernel logic when thp was
originally merged. I think it's primarily targeted to adjust the high
watermark so we could probably get the same behavior by special casing thp
with some scalar to the watermarks, but changing min_free_kbytes was
probably the easiest way to do it.