Re: [PATCH] x86/mm: use max memory block size with unaligned memory end

[Daniel Jordan]

On Thu, Jun 04, 2020 at 07:45:40PM +0200, David Hildenbrand wrote:
> On 04.06.20 19:22, Daniel Jordan wrote:
> > IMHO the root cause of this is really the small block size.  Building a cache
> > on top to avoid iterating over tons of small blocks seems like papering over
> > the problem, especially when one of the two affected paths in boot is a
> 
> The memory block size dictates your memory hot(un)plug granularity.

Indeed.

> E.g., on powerpc that's 16MB so they have *a lot* of memory blocks.
> That's why that's not papering over the problem. Increasing the memory
> block size isn't always the answer.

Ok.  If you don't mind, what's the purpose of hotplugging at that granularity?
I'm simply curious.

> > cautious check that might be ready to be removed by now[0]:
> 
> Yeah, we discussed that somewhere already. My change only highlighted
> the problem. And now that it's cheap, it can just stay unless there is a
> very good reason not to do it.

Agreed.

> > Yeah, but of course it's not as bad as it was now that it's fully parallelized.
> 
> Right. I also observed that computing if a zone is contiguous can be
> expensive.

That's right, I remember that.  It's on my list :)