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

Mel Gorman
2014-01-15T15:22:24Z

On Tue, Jan 14, 2014 at 04:35:33PM -0800, Andrew Morton wrote:
> > 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 logic from hugeadm where few people knew about it to the
kernel. The value is related to anti-fragmentation. With the recommended
setting the probability of mixing pages of different mobility within a
single pageblock is reduced. Very very superficially, it reduces the
number of instances the mm_page_alloc_extfrag tracepoint is triggered
with parameters that are considered to be severely fragmenting.

--
Mel Gorman
SUSE Labs