linux-kernel - [PATCH mm-stable] mm/hugetlb: set head flag before setting compound_order in __prep_compound_gigantic

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Date:   Mon, 12 Dec 2022 14:55:29 -0800
From:   Sidhartha Kumar <sidhartha.kumar@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, songmuchun@...edance.com,
        mike.kravetz@...cle.com, willy@...radead.org, tsahu@...ux.ibm.com,
        jhubbard@...dia.com, david@...hat.com,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>
Subject: [PATCH mm-stable] mm/hugetlb: set head flag before setting compound_order in __prep_compound_gigantic_folio

folio_set_compound_order() checks if the passed in folio is a large folio.
A large folio is indicated by the PG_head flag. Call __folio_set_head()
before setting the order.

Signed-off-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
Reported-by: David Hildenbrand <david@...hat.com>
---
Hi David, 
I tested this by doing:

echo 10 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
echo 0 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages

and checking dmesg. Let me know if there are other ways of testing
you would like to see run. 

Hi Andrew,
This can be folded into d1c6095572d0cf00c0cd30378639ff9387b34edd
mm/hugetlb: convert hugetlb prep functions to folios.

However, there is still ongoing discussion with this patch series,
specifically with patch 1 9fd330582b2f mm: add folio dtor and order setter
functions, so I'm not sure if this series should be a part of the 6.2 merge
window. I am planning to send a v6 within the next few days to implement
the suggested changes.

 mm/hugetlb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8c6fe2286814..7cdbcc22587b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1805,10 +1805,10 @@ static bool __prep_compound_gigantic_folio(struct folio *folio,
 	int nr_pages = 1 << order;
 	struct page *p;

-	/* we rely on prep_new_hugetlb_folio to set the destructor */
-	folio_set_compound_order(folio, order);
 	__folio_clear_reserved(folio);
 	__folio_set_head(folio);
+	/* we rely on prep_new_hugetlb_folio to set the destructor */
+	folio_set_compound_order(folio, order);
 	for (i = 0; i < nr_pages; i++) {
 		p = folio_page(folio, i);

-- 
2.38.1