linux-kernel - [PATCH v3 08/14] mm/khugepaged: Remove redundant pmd

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Message-ID: <a68175fd3a37e9b72cc82c1d63fd8b69691a85b5.1750323463.git-series.apopple@nvidia.com>
Date: Thu, 19 Jun 2025 18:58:00 +1000
From: Alistair Popple <apopple@...dia.com>
To: akpm@...ux-foundation.org
Cc: linux-mm@...ck.org,
	Alistair Popple <apopple@...dia.com>,
	gerald.schaefer@...ux.ibm.com,
	dan.j.williams@...el.com,
	jgg@...pe.ca,
	willy@...radead.org,
	david@...hat.com,
	linux-kernel@...r.kernel.org,
	nvdimm@...ts.linux.dev,
	linux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org,
	linux-xfs@...r.kernel.org,
	jhubbard@...dia.com,
	hch@....de,
	zhang.lyra@...il.com,
	debug@...osinc.com,
	bjorn@...nel.org,
	balbirs@...dia.com,
	lorenzo.stoakes@...cle.com,
	linux-arm-kernel@...ts.infradead.org,
	loongarch@...ts.linux.dev,
	linuxppc-dev@...ts.ozlabs.org,
	linux-riscv@...ts.infradead.org,
	linux-cxl@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	John@...ves.net,
	m.szyprowski@...sung.com,
	Jason Gunthorpe <jgg@...dia.com>
Subject: [PATCH v3 08/14] mm/khugepaged: Remove redundant pmd_devmap() check

The pmd_devmap() check in check_pmd_state() is redundant because the
only user of pmd_devmap were device dax and fs dax. However all callers
of check_pmd_state() first call thp_vma_allowable_order() to check if
the vma should be scanned. Except when called from a page fault this
always returns 0 for dax vma's, hence we would never expect to see a
pmd_devmap entry.

Signed-off-by: Alistair Popple <apopple@...dia.com>
Acked-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

---

Changes from v2:

 - Update commit message to better reflect why the check was redundant
---
 mm/khugepaged.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 15203ea..d45d08b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -945,8 +945,6 @@ static inline int check_pmd_state(pmd_t *pmd)
 		return SCAN_PMD_NULL;
 	if (pmd_trans_huge(pmde))
 		return SCAN_PMD_MAPPED;
-	if (pmd_devmap(pmde))
-		return SCAN_PMD_NULL;
 	if (pmd_bad(pmde))
 		return SCAN_PMD_NULL;
 	return SCAN_SUCCEED;
-- 
git-series 0.9.1