From: Matthew Wilcox <willy@infradead.org>
To: linux-mm@kvack.org
Cc: akpm@linuxfoundation.org, Matthew Wilcox <mawilcox@microsoft.com>
Subject: [PATCH 6/8] mm: Store compound_dtor / compound_order as bytes
Date: Wed, 20 Dec 2017 07:52:54 -0800 [thread overview]
Message-ID: <20171220155256.9841-7-willy@infradead.org> (raw)
In-Reply-To: <20171220155256.9841-1-willy@infradead.org>
From: Matthew Wilcox <mawilcox@microsoft.com>
Neither of these values get even close to 256; compound_dtor is
currently at a maximum of 3, and compound_order can't be over 64.
No machine has inefficient access to bytes since EV5, and while
those are still supported, we don't optimise for them any more.
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
---
include/linux/mm_types.h | 15 ++-------------
1 file changed, 2 insertions(+), 13 deletions(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5521c9799c50..1a3ba1f1605d 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -136,19 +136,8 @@ struct page {
unsigned long compound_head; /* If bit zero is set */
/* First tail page only */
-#ifdef CONFIG_64BIT
- /*
- * On 64 bit system we have enough space in struct page
- * to encode compound_dtor and compound_order with
- * unsigned int. It can help compiler generate better or
- * smaller code on some archtectures.
- */
- unsigned int compound_dtor;
- unsigned int compound_order;
-#else
- unsigned short int compound_dtor;
- unsigned short int compound_order;
-#endif
+ unsigned char compound_dtor;
+ unsigned char compound_order;
};
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
--
2.15.1
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next prev parent reply other threads:[~2017-12-20 15:53 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-20 15:52 [PATCH 0/8] Restructure struct page Matthew Wilcox
2017-12-20 15:52 ` [PATCH 1/8] mm: Align struct page more aesthetically Matthew Wilcox
2017-12-20 15:52 ` [PATCH 2/8] mm: De-indent struct page Matthew Wilcox
2017-12-20 15:52 ` [PATCH 3/8] mm: Remove misleading alignment claims Matthew Wilcox
2017-12-20 15:52 ` [PATCH 4/8] mm: Improve comment on page->mapping Matthew Wilcox
2017-12-20 15:52 ` [PATCH 5/8] mm: Introduce _slub_counter_t Matthew Wilcox
2017-12-20 15:52 ` Matthew Wilcox [this message]
2017-12-20 15:52 ` [PATCH 7/8] mm: Document how to use struct page Matthew Wilcox
2017-12-20 15:52 ` [PATCH 8/8] mm: Remove reference to PG_buddy Matthew Wilcox
2017-12-20 15:55 ` [PATCH 0/8] Restructure struct page Matthew Wilcox
-- strict thread matches above, loose matches on Subject: below --
2017-12-16 16:44 Matthew Wilcox
2017-12-16 16:44 ` [PATCH 6/8] mm: Store compound_dtor / compound_order as bytes Matthew Wilcox
2017-12-19 8:19 ` Michal Hocko
2017-12-19 12:49 ` Matthew Wilcox
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