Re: [PATCH] memory-hotplug: Fix bad area access on dissolve_free_huge_pages()

From: Michal Hocko
Date: Wed Sep 21 2016 - 08:05:30 EST

On Tue 20-09-16 10:43:13, Dave Hansen wrote:
> On 09/20/2016 08:52 AM, Rui Teng wrote:
> > On 9/20/16 10:53 PM, Dave Hansen wrote:
> ...
> >> That's good, but aren't we still left with a situation where we've
> >> offlined and dissolved the _middle_ of a gigantic huge page while the
> >> head page is still in place and online?
> >>
> >> That seems bad.
> >>
> > What about refusing to change the status for such memory block, if it
> > contains a huge page which larger than itself? (function
> > memory_block_action())
> How will this be visible to users, though? That sounds like you simply
> won't be able to offline memory with gigantic huge pages.

I might be missing something but Is this any different from a regular
failure when the memory cannot be freed? I mean
/sys/devices/system/memory/memory API doesn't give you any hint whether
the memory in the particular block is used and

Michal Hocko