From 1378a5ee451a5e87d0d8dd6356a0b7844db231f6 Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Fri, 14 Aug 2020 17:30:23 -0700
Subject: [PATCH] mm: store compound_nr as well as compound_order
Patch series "THP prep patches".
These are some generic cleanups and improvements, which I would like
merged into mmotm soon. The first one should be a performance improvement
for all users of compound pages, and the others are aimed at getting code
to compile away when CONFIG_TRANSPARENT_HUGEPAGE is disabled (ie small
systems). Also better documented / less confusing than the current prefix
mixture of compound, hpage and thp.
This patch (of 7):
This removes a few instructions from functions which need to know how many
pages are in a compound page. The storage used is either page->mapping on
64-bit or page->index on 32-bit. Both of these are fine to overlay on
tail pages.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Link: http://lkml.kernel.org/r/20200629151959.15779-1-willy@infradead.org
Link: http://lkml.kernel.org/r/20200629151959.15779-2-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
include/linux/mm.h | 5 ++++-
include/linux/mm_types.h | 1 +
mm/page_alloc.c | 5 +++--
3 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index e7602a3bcef1..10b1e6e5f885 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -922,12 +922,15 @@ static inline int compound_pincount(struct page *page)
static inline void set_compound_order(struct page *page, unsigned int order)
{
page[1].compound_order = order;
+ page[1].compound_nr = 1U << order;
}
/* Returns the number of pages in this potentially compound page. */
static inline unsigned long compound_nr(struct page *page)
{
- return 1UL << compound_order(page);
+ if (!PageHead(page))
+ return 1;
+ return page[1].compound_nr;
}
/* Returns the number of bytes in this potentially compound page. */
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 0277fbab7c93..496c3ff97cce 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -134,6 +134,7 @@ struct page {
unsigned char compound_dtor;
unsigned char compound_order;
atomic_t compound_mapcount;
+ unsigned int compound_nr; /* 1 << compound_order */
};
struct { /* Second tail page of compound page */
unsigned long _compound_pad_1; /* compound_head */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8b7d0ecf30b1..0e2bab486fea 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -666,8 +666,6 @@ void prep_compound_page(struct page *page, unsigned int order)
int i;
int nr_pages = 1 << order;
- set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
- set_compound_order(page, order);
__SetPageHead(page);
for (i = 1; i < nr_pages; i++) {
struct page *p = page + i;
@@ -675,6 +673,9 @@ void prep_compound_page(struct page *page, unsigned int order)
p->mapping = TAIL_MAPPING;
set_compound_head(p, page);
}
+
+ set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
+ set_compound_order(page, order);
atomic_set(compound_mapcount_ptr(page), -1);
if (hpage_pincount_available(page))
atomic_set(compound_pincount_ptr(page), 0);