linux-kernel - [PATCH v5 1/8] mm/huge_memory: only split PMD mapping when necessary in unmap

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Date: Mon, 26 Feb 2024 15:55:27 -0500
From: Zi Yan <zi.yan@...t.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
	linux-mm@...ck.org
Cc: Zi Yan <ziy@...dia.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	David Hildenbrand <david@...hat.com>,
	Yang Shi <shy828301@...il.com>,
	Yu Zhao <yuzhao@...gle.com>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Michal Koutný <mkoutny@...e.com>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	"Zach O'Keefe" <zokeefe@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: [PATCH v5 1/8] mm/huge_memory: only split PMD mapping when necessary in unmap_folio()

From: Zi Yan <ziy@...dia.com>

As multi-size THP support is added, not all THPs are PMD-mapped, thus
during a huge page split, there is no need to always split PMD mapping
in unmap_folio(). Make it conditional.

Signed-off-by: Zi Yan <ziy@...dia.com>
---
 mm/huge_memory.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 28341a5067fb..b20e535e874c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2727,11 +2727,14 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,
 
 static void unmap_folio(struct folio *folio)
 {
-	enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD |
-		TTU_SYNC | TTU_BATCH_FLUSH;
+	enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SYNC |
+		TTU_BATCH_FLUSH;
 
 	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
 
+	if (folio_test_pmd_mappable(folio))
+		ttu_flags |= TTU_SPLIT_HUGE_PMD;
+
 	/*
 	 * Anon pages need migration entries to preserve them, but file
 	 * pages can simply be left unmapped, then faulted back on demand.
-- 
2.43.0