linux-kernel - [RFC v2 3/4] mm: add largest_zero

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Message-ID: <20250724145001.487878-4-kernel@pankajraghav.com>
Date: Thu, 24 Jul 2025 16:50:00 +0200
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: Suren Baghdasaryan <surenb@...gle.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Borislav Petkov <bp@...en8.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Zi Yan <ziy@...dia.com>,
	Mike Rapoport <rppt@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Michal Hocko <mhocko@...e.com>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nico Pache <npache@...hat.com>,
	Dev Jain <dev.jain@....com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Jens Axboe <axboe@...nel.dk>
Cc: linux-kernel@...r.kernel.org,
	willy@...radead.org,
	linux-mm@...ck.org,
	x86@...nel.org,
	linux-block@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	"Darrick J . Wong" <djwong@...nel.org>,
	mcgrof@...nel.org,
	gost.dev@...sung.com,
	kernel@...kajraghav.com,
	hch@....de,
	Pankaj Raghav <p.raghav@...sung.com>
Subject: [RFC v2 3/4]  mm: add largest_zero_folio() routine

From: Pankaj Raghav <p.raghav@...sung.com>

Add largest_zero_folio() routine so that huge_zero_folio can be
used directly when CONFIG_STATIC_HUGE_ZERO_FOLIO is enabled. This will
return ZERO_PAGE folio if CONFIG_STATIC_HUGE_ZERO_FOLIO is disabled or
if we failed to allocate a huge_zero_folio.

Co-developed-by: David Hildenbrand <david@...hat.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
---
 include/linux/huge_mm.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 78ebceb61d0e..c44a6736704b 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -716,4 +716,21 @@ static inline int split_folio_to_order(struct folio *folio, int new_order)
 	return split_folio_to_list_to_order(folio, NULL, new_order);
 }
 
+/*
+ * largest_zero_folio - Get the largest zero size folio available
+ *
+ * This function will return huge_zero_folio if CONFIG_STATIC_HUGE_ZERO_FOLIO
+ * is enabled. Otherwise, a ZERO_PAGE folio is returned.
+ *
+ * Deduce the size of the folio with folio_size instead of assuming the
+ * folio size.
+ */
+static inline struct folio *largest_zero_folio(void)
+{
+	struct folio *folio = get_static_huge_zero_folio();
+
+	if (folio)
+		return folio;
+	return page_folio(ZERO_PAGE(0));
+}
 #endif /* _LINUX_HUGE_MM_H */
-- 
2.49.0