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From: Matthew Wilcox <willy@infradead.org>
To: linux-mm@kvack.org
Cc: "Matthew Wilcox" <mawilcox@microsoft.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	"Christoph Lameter" <cl@linux.com>,
	"Lai Jiangshan" <jiangshanlai@gmail.com>,
	"Pekka Enberg" <penberg@kernel.org>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"Jérôme Glisse" <jglisse@redhat.com>
Subject: [PATCH v5 06/17] mm: Move _refcount out of struct page union
Date: Fri,  4 May 2018 11:33:07 -0700	[thread overview]
Message-ID: <20180504183318.14415-7-willy@infradead.org> (raw)
In-Reply-To: <20180504183318.14415-1-willy@infradead.org>

From: Matthew Wilcox <mawilcox@microsoft.com>

Keeping the refcount in the union only encourages people to put
something else in the union which will overlap with _refcount and
eventually explode messily.  pahole reports no fields change location.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 include/linux/mm_types.h | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 23378a789af4..9828cd170251 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -113,7 +113,13 @@ struct page {
 		};
 	};
 
-	union {
+	union {		/* This union is 4 bytes in size. */
+		/*
+		 * If the page can be mapped to userspace, encodes the number
+		 * of times this page is referenced by a page table.
+		 */
+		atomic_t _mapcount;
+
 		/*
 		 * If the page is neither PageSlab nor mappable to userspace,
 		 * the value stored here may help determine what this page
@@ -124,22 +130,11 @@ struct page {
 
 		unsigned int active;		/* SLAB */
 		int units;			/* SLOB */
-
-		struct {			/* Page cache */
-			/*
-			 * Count of ptes mapped in mms, to show when
-			 * page is mapped & limit reverse map searches.
-			 */
-			atomic_t _mapcount;
-
-			/*
-			 * Usage count, *USE WRAPPER FUNCTION* when manual
-			 * accounting. See page_ref.h
-			 */
-			atomic_t _refcount;
-		};
 	};
 
+	/* Usage count. *DO NOT USE DIRECTLY*. See page_ref.h */
+	atomic_t _refcount;
+
 	/*
 	 * WARNING: bit 0 of the first word encode PageTail(). That means
 	 * the rest users of the storage space MUST NOT use the bit to
-- 
2.17.0

  parent reply	other threads:[~2018-05-04 18:33 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-04 18:33 [PATCH v5 00/17] Rearrange struct page Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 01/17] s390: Use _refcount for pgtables Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 02/17] mm: Split page_type out from _mapcount Matthew Wilcox
2018-05-14 14:33   ` Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 03/17] mm: Mark pages in use for page tables Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 04/17] mm: Switch s_mem and slab_cache in struct page Matthew Wilcox
2018-05-07 14:58   ` Christopher Lameter
2018-05-14 14:37   ` Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 05/17] mm: Move 'private' union within " Matthew Wilcox
2018-05-04 18:33 ` Matthew Wilcox [this message]
2018-05-04 18:33 ` [PATCH v5 07/17] mm: Combine first three unions in " Matthew Wilcox
2018-05-14 14:42   ` Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 08/17] mm: Use page->deferred_list Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 09/17] mm: Move lru union within struct page Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 10/17] mm: Combine LRU and main union in " Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 11/17] mm: Improve struct page documentation Matthew Wilcox
2018-05-15  9:22   ` Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 12/17] mm: Add pt_mm to struct page Matthew Wilcox
2018-05-15  9:27   ` Vlastimil Babka
2018-05-15 12:23     ` Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 13/17] mm: Add hmm_data " Matthew Wilcox
2018-05-15  9:32   ` Vlastimil Babka
2018-05-15 12:40     ` Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 14/17] slab,slub: Remove rcu_head size checks Matthew Wilcox
2018-05-15 11:30   ` Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 15/17] slub: Remove kmem_cache->reserved Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 16/17] slub: Remove 'reserved' file from sysfs Matthew Wilcox
2018-05-07 15:01   ` Christopher Lameter
2018-05-04 18:33 ` [PATCH v5 17/17] mm: Distinguish VMalloc pages Matthew Wilcox
2018-05-04 20:52 ` [PATCH v5 00/17] Rearrange struct page Andrew Morton
2018-05-04 21:25   ` Matthew Wilcox

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