Re: [PATCH 2/6] mm: memory_hotplug: use more folio in do_migrate_range()

[Matthew Wilcox <willy@infradead.org>]

On Wed, Mar 27, 2024 at 11:10:48AM -0400, Zi Yan wrote:
> On 27 Mar 2024, at 10:54, Matthew Wilcox wrote:
> > How much of this is safe without a refcount on the folio?
> 
> folio_to_pfn() should be fine, isolate_hugetlb() checks the folio
> under hugetlb_lock, but folio_nr_pages() might return a bogus number
> that makes pfn go beyond end_pfn and ends for loop early. The code
> below increases the refcount, so it might be better to move this
> part of the code after refcount is increased.

I really want to instill a little bit of fear in Kefeng.

This is all really subtle code because it's running without a refcount.
I've mostly stayed away from it because I know that I don't know what
I'm doing.  Kefeng has no idea that he doesn't know what he's doing.

And so we get these patches, and they're sometimes subtly wrong, and it
takes a lot of arguing and revision and thinking and Kefeng is doing
very little of the thinking part!

Kefeng, please stick to working on code that you understand.  Or take
the time to learn code you don't understand before sending patches to
it.  This kind of Leeroy Jenkins approach to development is not good.