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Date: Mon, 28 Mar 2016 15:30:01 +0900
From: js1304@...il.com
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Hugh Dickins <hughd@...gle.com>,
Johannes Berg <johannes@...solutions.net>,
"David S. Miller" <davem@...emloft.net>,
Sunil Goutham <sgoutham@...ium.com>,
Chris Metcalf <cmetcalf@...lanox.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: [PATCH v2 2/2] mm: rename _count, field of the struct page, to _refcount
From: Joonsoo Kim <iamjoonsoo.kim@....com>
Many developer already know that field for reference count of
the struct page is _count and atomic type. They would try to handle it
directly and this could break the purpose of page reference count
tracepoint. To prevent direct _count modification, this patch rename it
to _refcount and add warning message on the code. After that, developer
who need to handle reference count will find that field should not be
accessed directly.
v2: change more _count usages to _refcount
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
---
arch/tile/mm/init.c | 2 +-
include/linux/mm_types.h | 8 ++++++--
include/linux/page_ref.h | 26 +++++++++++++-------------
kernel/kexec_core.c | 2 +-
4 files changed, 21 insertions(+), 17 deletions(-)
diff --git a/arch/tile/mm/init.c b/arch/tile/mm/init.c
index a0582b7..adce254 100644
--- a/arch/tile/mm/init.c
+++ b/arch/tile/mm/init.c
@@ -679,7 +679,7 @@ static void __init init_free_pfn_range(unsigned long start, unsigned long end)
* Hacky direct set to avoid unnecessary
* lock take/release for EVERY page here.
*/
- p->_count.counter = 0;
+ p->_refcount.counter = 0;
p->_mapcount.counter = -1;
}
init_page_count(page);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 944b2b3..9e8eb5a 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -97,7 +97,11 @@ struct page {
};
int units; /* SLOB */
};
- atomic_t _count; /* Usage count, see below. */
+ /*
+ * Usage count, *USE WRAPPER FUNCTION*
+ * when manual accounting. See page_ref.h
+ */
+ atomic_t _refcount;
};
unsigned int active; /* SLAB */
};
@@ -248,7 +252,7 @@ struct page_frag_cache {
__u32 offset;
#endif
/* we maintain a pagecount bias, so that we dont dirty cache line
- * containing page->_count every time we allocate a fragment.
+ * containing page->_refcount every time we allocate a fragment.
*/
unsigned int pagecnt_bias;
bool pfmemalloc;
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
index e596d5d9..8b5e0a9 100644
--- a/include/linux/page_ref.h
+++ b/include/linux/page_ref.h
@@ -63,17 +63,17 @@ static inline void __page_ref_unfreeze(struct page *page, int v)
static inline int page_ref_count(struct page *page)
{
- return atomic_read(&page->_count);
+ return atomic_read(&page->_refcount);
}
static inline int page_count(struct page *page)
{
- return atomic_read(&compound_head(page)->_count);
+ return atomic_read(&compound_head(page)->_refcount);
}
static inline void set_page_count(struct page *page, int v)
{
- atomic_set(&page->_count, v);
+ atomic_set(&page->_refcount, v);
if (page_ref_tracepoint_active(__tracepoint_page_ref_set))
__page_ref_set(page, v);
}
@@ -89,35 +89,35 @@ static inline void init_page_count(struct page *page)
static inline void page_ref_add(struct page *page, int nr)
{
- atomic_add(nr, &page->_count);
+ atomic_add(nr, &page->_refcount);
if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
__page_ref_mod(page, nr);
}
static inline void page_ref_sub(struct page *page, int nr)
{
- atomic_sub(nr, &page->_count);
+ atomic_sub(nr, &page->_refcount);
if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
__page_ref_mod(page, -nr);
}
static inline void page_ref_inc(struct page *page)
{
- atomic_inc(&page->_count);
+ atomic_inc(&page->_refcount);
if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
__page_ref_mod(page, 1);
}
static inline void page_ref_dec(struct page *page)
{
- atomic_dec(&page->_count);
+ atomic_dec(&page->_refcount);
if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
__page_ref_mod(page, -1);
}
static inline int page_ref_sub_and_test(struct page *page, int nr)
{
- int ret = atomic_sub_and_test(nr, &page->_count);
+ int ret = atomic_sub_and_test(nr, &page->_refcount);
if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_test))
__page_ref_mod_and_test(page, -nr, ret);
@@ -126,7 +126,7 @@ static inline int page_ref_sub_and_test(struct page *page, int nr)
static inline int page_ref_dec_and_test(struct page *page)
{
- int ret = atomic_dec_and_test(&page->_count);
+ int ret = atomic_dec_and_test(&page->_refcount);
if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_test))
__page_ref_mod_and_test(page, -1, ret);
@@ -135,7 +135,7 @@ static inline int page_ref_dec_and_test(struct page *page)
static inline int page_ref_dec_return(struct page *page)
{
- int ret = atomic_dec_return(&page->_count);
+ int ret = atomic_dec_return(&page->_refcount);
if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_return))
__page_ref_mod_and_return(page, -1, ret);
@@ -144,7 +144,7 @@ static inline int page_ref_dec_return(struct page *page)
static inline int page_ref_add_unless(struct page *page, int nr, int u)
{
- int ret = atomic_add_unless(&page->_count, nr, u);
+ int ret = atomic_add_unless(&page->_refcount, nr, u);
if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_unless))
__page_ref_mod_unless(page, nr, ret);
@@ -153,7 +153,7 @@ static inline int page_ref_add_unless(struct page *page, int nr, int u)
static inline int page_ref_freeze(struct page *page, int count)
{
- int ret = likely(atomic_cmpxchg(&page->_count, count, 0) == count);
+ int ret = likely(atomic_cmpxchg(&page->_refcount, count, 0) == count);
if (page_ref_tracepoint_active(__tracepoint_page_ref_freeze))
__page_ref_freeze(page, count, ret);
@@ -165,7 +165,7 @@ static inline void page_ref_unfreeze(struct page *page, int count)
VM_BUG_ON_PAGE(page_count(page) != 0, page);
VM_BUG_ON(count == 0);
- atomic_set(&page->_count, count);
+ atomic_set(&page->_refcount, count);
if (page_ref_tracepoint_active(__tracepoint_page_ref_unfreeze))
__page_ref_unfreeze(page, count);
}
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index f826e11..e0e95b0 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -1410,7 +1410,7 @@ static int __init crash_save_vmcoreinfo_init(void)
VMCOREINFO_STRUCT_SIZE(list_head);
VMCOREINFO_SIZE(nodemask_t);
VMCOREINFO_OFFSET(page, flags);
- VMCOREINFO_OFFSET(page, _count);
+ VMCOREINFO_OFFSET(page, _refcount);
VMCOREINFO_OFFSET(page, mapping);
VMCOREINFO_OFFSET(page, lru);
VMCOREINFO_OFFSET(page, _mapcount);
--
1.9.1
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