Re: [PATCH v3 31/35] lib: add memory allocations report in show_mem()

[Kent Overstreet]

On Thu, Feb 15, 2024 at 10:54:53PM +0100, Michal Hocko wrote:
> On Thu 15-02-24 15:33:30, Kent Overstreet wrote:
> > If we want this report to be 100% reliable, then yes the preallocated
> > buffer makes sense - but I don't think 100% makes sense here; I think we
> > can accept ~99% and give back that 4k.
> 
> Think about that from the memory reserves consumers. The atomic reserve
> is a scarse resource and now you want to use it for debugging purposes
> for which you could have preallocated.

_Memory_ is a finite resource that we shouldn't be using unnecessarily. 

We don't need this for the entire time we're under memory pressure; just
the short duration it takes to generate the report, then it's back
available for other users.

You would have us dedicate 4k, from system bootup, that can never be
used by other users.

Again: this makes no sense. The whole point of having watermarks and
shared reserves is so that every codepath doesn't have to have its own
dedicated, private reserve, so that we can make better use of a shared
finite resource.