Re: [PATCH v4 2/2] mm: Init page count in reserve_bootmem_region when MEMINIT_EARLY

[Yajun Deng]

On 2023/10/5 13:06, Mike Rapoport wrote:
> On Tue, Oct 03, 2023 at 10:38:09PM +0800, Yajun Deng wrote:
> > On 2023/10/2 19:25, David Hildenbrand wrote:
> > > On 02.10.23 13:10, Mike Rapoport wrote:
> > > > > > That 'if' breaks the invariant that __free_pages_core is
> > > > > > always called for
> > > > > > pages with initialized page count. Adding it may lead to
> > > > > > subtle bugs and
> > > > > > random memory corruption so we don't want to add it at the
> > > > > > first place.
> > > > > As long as we have to special-case memory hotplug, we know that we are
> > > > > always coming via generic_online_page() in that case. We could
> > > > > either move
> > > > > some logic over there, or let __free_pages_core() know what it
> > > > > should do.
> > > > Looks like the patch rather special cases MEMINIT_EARLY, although I
> > > > didn't
> > > > check throughfully other code paths.
> > > > Anyway, relying on page_count() to be correct in different ways for
> > > > different callers of __free_pages_core() does not sound right to me.
> > > Absolutely agreed.
> > I already sent v5  a few days ago. Comments, please...
> Does it address all the feedback from this thread?

Except hotplug. As far as I konw, we only clear page count in 
MEMINIT_EARLY and all tail pages in compound page.

So adding 'if (page_count(page))' will have no actual effect for other 
case. According to previous data, it didn't

become slower in hotplug.