Re: [v4] mm: khugepaged: avoid overriding min_free_kbytes set by user

[Kirill A. Shutemov]

On Mon, Sep 21, 2020 at 12:07:23PM -0700, Vijay Balakrishna wrote:
> > 
> > I would recommend reposting the patch which adds heuristic for THP (if
> > THP is enabled) into the hotplug path, arguing with the consistency and
> > surprising results when adding memory decreases the value.
> 
> I hope my reposted patch
> ([v3 1/2] mm: khugepaged: recalculate min_free_kbytes after memory hotplug
> as expected by khugepaged)
> change log is ok:
> 
> When memory is hotplug added or removed the min_free_kbytes must be
> recalculated based on what is expected by khugepaged.  Currently
> after hotplug, min_free_kbytes will be set to a lower default and higher
> default set when THP enabled is lost.  This change restores min_free_kbytes
> as expected for THP consumers.

Any scenario when hotremove would result in changing min_free_kbytes?

> > Your initial
> > problem is in sizing as mentioned in other email thread and you should
> > be investigating more but this inconsistency might really come as a
> > surprise.
> > 
> > All that if Kirill is reconsidering his initial position of course.
> > 
> 
> Kirill, can you comment or share your opinion?

Looking again, never decreasing min_free_kbytes is the most reasonable
policy. Sorry for the noise.

But I would like to see a scenario when hotremov will end up changing
min_free_kbytes. It's not obvious to me.

-- 
 Kirill A. Shutemov