linux-kernel - [PATCH v2] pgtable: do not expose

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Message-ID: <ZVzQkTueDRSJ76me@tuxmaker.boeblingen.de.ibm.com>
Date:   Tue, 21 Nov 2023 16:45:21 +0100
From:   Alexander Gordeev <agordeev@...ux.ibm.com>
To:     Heiko Carstens <hca@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Vishal Moola <vishal.moola@...il.com>, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
Subject: [PATCH v2] pgtable: do not expose _refcount field via ptdesc

Since commit d08d4e7cd6bf ("s390/mm: use full 4KB page for 2KB PTE")
_refcount field is not used for fragmented page tracking on s390 and
there is no other code left that accesses this field explicitly.

Suggested-by: Heiko Carstens <hca@...ux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@...ux.ibm.com>
---
 include/linux/mm_types.h | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 957ce38768b2..ce0cfc6e4d94 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -401,11 +401,11 @@ FOLIO_MATCH(compound_head, _head_2a);
  * @pmd_huge_pte:     Protected by ptdesc->ptl, used for THPs.
  * @__page_mapping:   Aliases with page->mapping. Unused for page tables.
  * @pt_mm:            Used for x86 pgds.
- * @pt_frag_refcount: For fragmented page table tracking. Powerpc and s390 only.
+ * @pt_frag_refcount: For fragmented page table tracking. Powerpc only.
  * @_pt_pad_2:        Padding to ensure proper alignment.
  * @ptl:              Lock for the page table.
  * @__page_type:      Same as page->page_type. Unused for page tables.
- * @_refcount:        Same as page refcount. Used for s390 page tables.
+ * @_pt_pad_3:        Padding that aliases with page's refcount.
  * @pt_memcg_data:    Memcg data. Tracked for page tables here.
  *
  * This struct overlays struct page for now. Do not modify without a good
@@ -438,7 +438,7 @@ struct ptdesc {
 #endif
 	};
 	unsigned int __page_type;
-	atomic_t _refcount;
+	unsigned int _pt_pad_3;
 #ifdef CONFIG_MEMCG
 	unsigned long pt_memcg_data;
 #endif
@@ -452,7 +452,6 @@ TABLE_MATCH(compound_head, _pt_pad_1);
 TABLE_MATCH(mapping, __page_mapping);
 TABLE_MATCH(rcu_head, pt_rcu_head);
 TABLE_MATCH(page_type, __page_type);
-TABLE_MATCH(_refcount, _refcount);
 #ifdef CONFIG_MEMCG
 TABLE_MATCH(memcg_data, pt_memcg_data);
 #endif
-- 
2.39.2