Re: [PATCH] mm: always consider THP when adjusting min_free_kbytes

[Matthew Wilcox]

On Wed, Feb 05, 2020 at 05:36:44PM -0800, Mike Kravetz wrote:
> The value of min_free_kbytes is calculated in two routines:
> 1) init_per_zone_wmark_min based on available memory
> 2) set_recommended_min_free_kbytes may reserve extra space for
>    THP allocations
> 
> In both of these routines, a user defined min_free_kbytes value will
> be overwritten if the value calculated in the code is larger. No message
> is logged if the user value is overwritten.
> 
> Change code to never overwrite user defined value.  However, do log a
> message (once per value) showing the value calculated in code.

But what if the user set min_free_kbytes to, say, half of system memory,
and then hot-unplugs three quarters of their memory?  I think the kernel
should protect itself against such foolishness.