linux-kernel - [RFC 2/8] mm/hugetlb: remove useless set_page

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Date:   Tue, 26 Oct 2021 17:38:16 +0000
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-m68k@...ts.linux-m68k.org,
        anshuman.khandual@....com, willy@...radead.org,
        akpm@...ux-foundation.org, william.kucharski@...cle.com,
        mike.kravetz@...cle.com, vbabka@...e.cz, geert@...ux-m68k.org,
        schmitzmic@...il.com, rostedt@...dmis.org, mingo@...hat.com,
        hannes@...xchg.org, guro@...com, songmuchun@...edance.com,
        weixugc@...gle.com, gthelen@...gle.com
Subject: [RFC 2/8] mm/hugetlb: remove useless set_page_count()

prep_compound_gigantic_page() calls set_page_count(0, p), but it is not
needed because page_ref_freeze(p, 1) already sets refcount to 0.

Using, set_page_count() is dangerous, because it unconditionally resets
refcount from the current value to unrestrained value, and therefore
should be minimized.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 mm/hugetlb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 95dc7b83381f..7e3996c8b696 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1707,7 +1707,7 @@ static bool prep_compound_gigantic_page(struct page *page, unsigned int order)
 			pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n");
 			goto out_error;
 		}
-		set_page_count(p, 0);
+		VM_BUG_ON_PAGE(page_count(p), p);
 		set_compound_head(p, page);
 	}
 	atomic_set(compound_mapcount_ptr(page), -1);
-- 
2.33.0.1079.g6e70778dc9-goog