Re: [PATCH 4/4] mm/page_alloc: no need to ClearPageReserved on giving page to buddy system

[Wei Yang <richard.weiyang@gmail.com>]

On Sat, Jun 29, 2024 at 08:28:30AM +0200, David Hildenbrand wrote:
>On 29.06.24 08:25, David Hildenbrand wrote:
>> On 29.06.24 03:33, Wei Yang wrote:
>> > Function __free_pages_core() is only used in the following two cases to
>> > put page to buddy system:
>> > 
>> > * free bootmem
>> > * free hot-add memory
>> > 
>> > After the above cleanup, there is no case to free page with PG_reserved
>> > set. Let's remove the clear operation.
>> > 
>> > The page initialization time shows 6.5% faster with a 6G qemu virtual
>> > machine.
>> > 
>> > Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> > CC: David Hildenbrand <david@redhat.com>
>> > CC: Mike Rapoport (IBM) <rppt@kernel.org>
>> > ---
>> >    mm/page_alloc.c | 2 --
>> >    1 file changed, 2 deletions(-)
>> > 
>> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> > index 51a47db375b6..bc7316744a34 100644
>> > --- a/mm/page_alloc.c
>> > +++ b/mm/page_alloc.c
>> > @@ -1232,10 +1232,8 @@ void __meminit __free_pages_core(struct page *page, unsigned int order)
>> >    	prefetchw(p);
>> >    	for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
>> >    		prefetchw(p + 1);
>> > -		__ClearPageReserved(p);
>> >    		set_page_count(p, 0);
>> >    	}
>> > -	__ClearPageReserved(p);
>> >    	set_page_count(p, 0);
>> >    	atomic_long_add(nr_pages, &page_zone(page)->managed_pages);
>> 
>> Again see mm/mm-stable where that code changed.
>> 
>> I think we can still get reserved pages here, for example via
>> kmsan_memblock_free_pages().
>> 

You mean ZONDE_DEVICE pages?

If yes, I think the normal memblock_free_pages() still could get reserved pages.
Am I right?

>
>Sorry, I meant kmsan_memblock_discard().

Yep.

>-- 
>Cheers,
>
>David / dhildenb

-- 
Wei Yang
Help you, Help me