* [PATCHv4 1/7] mm: drop page->slab_page
2015-08-27 13:59 [PATCHv4 0/7] Fix compound_head() race Kirill A. Shutemov
@ 2015-08-27 13:59 ` Kirill A. Shutemov
2015-08-27 13:59 ` [PATCHv4 2/7] slub: use page->rcu_head instead of page->lru plus cast Kirill A. Shutemov
` (5 subsequent siblings)
6 siblings, 0 replies; 11+ messages in thread
From: Kirill A. Shutemov @ 2015-08-27 13:59 UTC (permalink / raw)
To: Andrew Morton, Hugh Dickins
Cc: Andrea Arcangeli, Dave Hansen, Vlastimil Babka, Johannes Weiner,
Michal Hocko, David Rientjes, linux-kernel, linux-mm,
Kirill A. Shutemov, Joonsoo Kim, Andi Kleen
Since 8456a648cf44 ("slab: use struct page for slab management") nobody
uses slab_page field in struct page.
Let's drop it.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andi Kleen <ak@linux.intel.com>
---
include/linux/mm_types.h | 1 -
mm/slab.c | 17 +++--------------
2 files changed, 3 insertions(+), 15 deletions(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 0038ac7466fd..58620ac7f15c 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -140,7 +140,6 @@ struct page {
#endif
};
- struct slab *slab_page; /* slab fields */
struct rcu_head rcu_head; /* Used by SLAB
* when destroying via RCU
*/
diff --git a/mm/slab.c b/mm/slab.c
index 200e22412a16..649044f26e5d 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1888,21 +1888,10 @@ static void slab_destroy(struct kmem_cache *cachep, struct page *page)
freelist = page->freelist;
slab_destroy_debugcheck(cachep, page);
- if (unlikely(cachep->flags & SLAB_DESTROY_BY_RCU)) {
- struct rcu_head *head;
-
- /*
- * RCU free overloads the RCU head over the LRU.
- * slab_page has been overloeaded over the LRU,
- * however it is not used from now on so that
- * we can use it safely.
- */
- head = (void *)&page->rcu_head;
- call_rcu(head, kmem_rcu_free);
-
- } else {
+ if (unlikely(cachep->flags & SLAB_DESTROY_BY_RCU))
+ call_rcu(&page->rcu_head, kmem_rcu_free);
+ else
kmem_freepages(cachep, page);
- }
/*
* From now on, we don't use freelist
--
2.5.0
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^ permalink raw reply related [flat|nested] 11+ messages in thread* [PATCHv4 2/7] slub: use page->rcu_head instead of page->lru plus cast
2015-08-27 13:59 [PATCHv4 0/7] Fix compound_head() race Kirill A. Shutemov
2015-08-27 13:59 ` [PATCHv4 1/7] mm: drop page->slab_page Kirill A. Shutemov
@ 2015-08-27 13:59 ` Kirill A. Shutemov
2015-08-27 13:59 ` [PATCHv4 3/7] zsmalloc: use page->private instead of page->first_page Kirill A. Shutemov
` (4 subsequent siblings)
6 siblings, 0 replies; 11+ messages in thread
From: Kirill A. Shutemov @ 2015-08-27 13:59 UTC (permalink / raw)
To: Andrew Morton, Hugh Dickins
Cc: Andrea Arcangeli, Dave Hansen, Vlastimil Babka, Johannes Weiner,
Michal Hocko, David Rientjes, linux-kernel, linux-mm,
Kirill A. Shutemov, Christoph Lameter
We have properly typed page->rcu_head, no need to cast page->lru.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Christoph Lameter <cl@linux.com>
---
mm/slub.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 816df0016555..869642d03b22 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1510,10 +1510,7 @@ static void free_slab(struct kmem_cache *s, struct page *page)
VM_BUG_ON(s->reserved != sizeof(*head));
head = page_address(page) + offset;
} else {
- /*
- * RCU free overloads the RCU head over the LRU
- */
- head = (void *)&page->lru;
+ head = &page->rcu_head;
}
call_rcu(head, rcu_free_slab);
--
2.5.0
--
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^ permalink raw reply related [flat|nested] 11+ messages in thread* [PATCHv4 3/7] zsmalloc: use page->private instead of page->first_page
2015-08-27 13:59 [PATCHv4 0/7] Fix compound_head() race Kirill A. Shutemov
2015-08-27 13:59 ` [PATCHv4 1/7] mm: drop page->slab_page Kirill A. Shutemov
2015-08-27 13:59 ` [PATCHv4 2/7] slub: use page->rcu_head instead of page->lru plus cast Kirill A. Shutemov
@ 2015-08-27 13:59 ` Kirill A. Shutemov
2015-08-31 1:30 ` Sergey Senozhatsky
2015-08-27 13:59 ` [PATCHv4 4/7] mm: pack compound_dtor and compound_order into one word in struct page Kirill A. Shutemov
` (3 subsequent siblings)
6 siblings, 1 reply; 11+ messages in thread
From: Kirill A. Shutemov @ 2015-08-27 13:59 UTC (permalink / raw)
To: Andrew Morton, Hugh Dickins
Cc: Andrea Arcangeli, Dave Hansen, Vlastimil Babka, Johannes Weiner,
Michal Hocko, David Rientjes, linux-kernel, linux-mm,
Kirill A. Shutemov
We are going to rework how compound_head() work. It will not use
page->first_page as we have it now.
The only other user of page->first_page beyond compound pages is
zsmalloc.
Let's use page->private instead of page->first_page here. It occupies
the same storage space.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/zsmalloc.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 0a7f81aa2249..6a092de6b636 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -16,7 +16,7 @@
* struct page(s) to form a zspage.
*
* Usage of struct page fields:
- * page->first_page: points to the first component (0-order) page
+ * page->private: points to the first component (0-order) page
* page->index (union with page->freelist): offset of the first object
* starting in this page. For the first page, this is
* always 0, so we use this field (aka freelist) to point
@@ -26,8 +26,7 @@
*
* For _first_ page only:
*
- * page->private (union with page->first_page): refers to the
- * component page after the first page
+ * page->private: refers to the component page after the first page
* If the page is first_page for huge object, it stores handle.
* Look at size_class->huge.
* page->freelist: points to the first free object in zspage.
@@ -770,7 +769,7 @@ static struct page *get_first_page(struct page *page)
if (is_first_page(page))
return page;
else
- return page->first_page;
+ return (struct page *)page_private(page);
}
static struct page *get_next_page(struct page *page)
@@ -955,7 +954,7 @@ static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
* Allocate individual pages and link them together as:
* 1. first page->private = first sub-page
* 2. all sub-pages are linked together using page->lru
- * 3. each sub-page is linked to the first page using page->first_page
+ * 3. each sub-page is linked to the first page using page->private
*
* For each size class, First/Head pages are linked together using
* page->lru. Also, we set PG_private to identify the first page
@@ -980,7 +979,7 @@ static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
if (i == 1)
set_page_private(first_page, (unsigned long)page);
if (i >= 1)
- page->first_page = first_page;
+ set_page_private(page, (unsigned long)first_page);
if (i >= 2)
list_add(&page->lru, &prev_page->lru);
if (i == class->pages_per_zspage - 1) /* last page */
--
2.5.0
--
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^ permalink raw reply related [flat|nested] 11+ messages in thread* Re: [PATCHv4 3/7] zsmalloc: use page->private instead of page->first_page
2015-08-27 13:59 ` [PATCHv4 3/7] zsmalloc: use page->private instead of page->first_page Kirill A. Shutemov
@ 2015-08-31 1:30 ` Sergey Senozhatsky
0 siblings, 0 replies; 11+ messages in thread
From: Sergey Senozhatsky @ 2015-08-31 1:30 UTC (permalink / raw)
To: Kirill A. Shutemov
Cc: Andrew Morton, Hugh Dickins, Andrea Arcangeli, Dave Hansen,
Vlastimil Babka, Johannes Weiner, Michal Hocko, David Rientjes,
linux-kernel, linux-mm
On (08/27/15 16:59), Kirill A. Shutemov wrote:
> We are going to rework how compound_head() work. It will not use
> page->first_page as we have it now.
>
> The only other user of page->first_page beyond compound pages is
> zsmalloc.
>
> Let's use page->private instead of page->first_page here. It occupies
> the same storage space.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
-ss
--
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^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCHv4 4/7] mm: pack compound_dtor and compound_order into one word in struct page
2015-08-27 13:59 [PATCHv4 0/7] Fix compound_head() race Kirill A. Shutemov
` (2 preceding siblings ...)
2015-08-27 13:59 ` [PATCHv4 3/7] zsmalloc: use page->private instead of page->first_page Kirill A. Shutemov
@ 2015-08-27 13:59 ` Kirill A. Shutemov
2015-08-27 13:59 ` [PATCHv4 5/7] mm: make compound_head() robust Kirill A. Shutemov
` (2 subsequent siblings)
6 siblings, 0 replies; 11+ messages in thread
From: Kirill A. Shutemov @ 2015-08-27 13:59 UTC (permalink / raw)
To: Andrew Morton, Hugh Dickins
Cc: Andrea Arcangeli, Dave Hansen, Vlastimil Babka, Johannes Weiner,
Michal Hocko, David Rientjes, linux-kernel, linux-mm,
Kirill A. Shutemov
The patch halves space occupied by compound_dtor and compound_order in
struct page.
For compound_order, it's trivial long -> short conversion.
For get_compound_page_dtor(), we now use hardcoded table for destructor
lookup and store its index in the struct page instead of direct pointer
to destructor. It shouldn't be a big trouble to maintain the table: we
have only two destructor and NULL currently.
This patch free up one word in tail pages for reuse. This is preparation
for the next patch.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Michal Hocko <mhocko@suse.com>
---
include/linux/mm.h | 24 +++++++++++++++++++-----
include/linux/mm_types.h | 6 ++----
mm/hugetlb.c | 8 ++++----
mm/page_alloc.c | 11 ++++++++++-
4 files changed, 35 insertions(+), 14 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2e872f92dbac..2cfe6051574c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -575,18 +575,32 @@ int split_free_page(struct page *page);
/*
* Compound pages have a destructor function. Provide a
* prototype for that function and accessor functions.
- * These are _only_ valid on the head of a PG_compound page.
+ * These are _only_ valid on the head of a compound page.
*/
+typedef void compound_page_dtor(struct page *);
+
+/* Keep the enum in sync with compound_page_dtors array in mm/page_alloc.c */
+enum compound_dtor_id {
+ NULL_COMPOUND_DTOR,
+ COMPOUND_PAGE_DTOR,
+#ifdef CONFIG_HUGETLB_PAGE
+ HUGETLB_PAGE_DTOR,
+#endif
+ NR_COMPOUND_DTORS,
+};
+extern compound_page_dtor * const compound_page_dtors[];
static inline void set_compound_page_dtor(struct page *page,
- compound_page_dtor *dtor)
+ enum compound_dtor_id compound_dtor)
{
- page[1].compound_dtor = dtor;
+ VM_BUG_ON_PAGE(compound_dtor >= NR_COMPOUND_DTORS, page);
+ page[1].compound_dtor = compound_dtor;
}
static inline compound_page_dtor *get_compound_page_dtor(struct page *page)
{
- return page[1].compound_dtor;
+ VM_BUG_ON_PAGE(page[1].compound_dtor >= NR_COMPOUND_DTORS, page);
+ return compound_page_dtors[page[1].compound_dtor];
}
static inline int compound_order(struct page *page)
@@ -596,7 +610,7 @@ static inline int compound_order(struct page *page)
return page[1].compound_order;
}
-static inline void set_compound_order(struct page *page, unsigned long order)
+static inline void set_compound_order(struct page *page, unsigned int order)
{
page[1].compound_order = order;
}
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 58620ac7f15c..408a54563f65 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -28,8 +28,6 @@ struct mem_cgroup;
IS_ENABLED(CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK))
#define ALLOC_SPLIT_PTLOCKS (SPINLOCK_SIZE > BITS_PER_LONG/8)
-typedef void compound_page_dtor(struct page *);
-
/*
* Each physical page in the system has a struct page associated with
* it to keep track of whatever it is we are using the page for at the
@@ -145,8 +143,8 @@ struct page {
*/
/* First tail page of compound page */
struct {
- compound_page_dtor *compound_dtor;
- unsigned long compound_order;
+ unsigned short int compound_dtor;
+ unsigned short int compound_order;
};
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a8c3087089d8..8ea74caa1fa8 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -969,7 +969,7 @@ static void update_and_free_page(struct hstate *h, struct page *page)
1 << PG_writeback);
}
VM_BUG_ON_PAGE(hugetlb_cgroup_from_page(page), page);
- set_compound_page_dtor(page, NULL);
+ set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
set_page_refcounted(page);
if (hstate_is_gigantic(h)) {
destroy_compound_gigantic_page(page, huge_page_order(h));
@@ -1065,7 +1065,7 @@ void free_huge_page(struct page *page)
static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
{
INIT_LIST_HEAD(&page->lru);
- set_compound_page_dtor(page, free_huge_page);
+ set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
spin_lock(&hugetlb_lock);
set_hugetlb_cgroup(page, NULL);
h->nr_huge_pages++;
@@ -1117,7 +1117,7 @@ int PageHuge(struct page *page)
return 0;
page = compound_head(page);
- return get_compound_page_dtor(page) == free_huge_page;
+ return page[1].compound_dtor == HUGETLB_PAGE_DTOR;
}
EXPORT_SYMBOL_GPL(PageHuge);
@@ -1314,7 +1314,7 @@ static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
if (page) {
INIT_LIST_HEAD(&page->lru);
r_nid = page_to_nid(page);
- set_compound_page_dtor(page, free_huge_page);
+ set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
set_hugetlb_cgroup(page, NULL);
/*
* We incremented the global counters already
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index df959b7d6085..c6733cc3cbce 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -208,6 +208,15 @@ static char * const zone_names[MAX_NR_ZONES] = {
"Movable",
};
+static void free_compound_page(struct page *page);
+compound_page_dtor * const compound_page_dtors[] = {
+ NULL,
+ free_compound_page,
+#ifdef CONFIG_HUGETLB_PAGE
+ free_huge_page,
+#endif
+};
+
int min_free_kbytes = 1024;
int user_min_free_kbytes = -1;
@@ -437,7 +446,7 @@ void prep_compound_page(struct page *page, unsigned long order)
int i;
int nr_pages = 1 << order;
- set_compound_page_dtor(page, free_compound_page);
+ set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
set_compound_order(page, order);
__SetPageHead(page);
for (i = 1; i < nr_pages; i++) {
--
2.5.0
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^ permalink raw reply related [flat|nested] 11+ messages in thread* [PATCHv4 5/7] mm: make compound_head() robust
2015-08-27 13:59 [PATCHv4 0/7] Fix compound_head() race Kirill A. Shutemov
` (3 preceding siblings ...)
2015-08-27 13:59 ` [PATCHv4 4/7] mm: pack compound_dtor and compound_order into one word in struct page Kirill A. Shutemov
@ 2015-08-27 13:59 ` Kirill A. Shutemov
2015-08-27 15:21 ` Michal Hocko
2015-08-27 13:59 ` [PATCHv4 6/7] mm: use 'unsigned int' for page order Kirill A. Shutemov
2015-08-27 13:59 ` [PATCHv4 7/7] mm: use 'unsigned int' for compound_dtor/compound_order on 64BIT Kirill A. Shutemov
6 siblings, 1 reply; 11+ messages in thread
From: Kirill A. Shutemov @ 2015-08-27 13:59 UTC (permalink / raw)
To: Andrew Morton, Hugh Dickins
Cc: Andrea Arcangeli, Dave Hansen, Vlastimil Babka, Johannes Weiner,
Michal Hocko, David Rientjes, linux-kernel, linux-mm,
Kirill A. Shutemov, Paul E. McKenney
Hugh has pointed that compound_head() call can be unsafe in some
context. There's one example:
CPU0 CPU1
isolate_migratepages_block()
page_count()
compound_head()
!!PageTail() == true
put_page()
tail->first_page = NULL
head = tail->first_page
alloc_pages(__GFP_COMP)
prep_compound_page()
tail->first_page = head
__SetPageTail(p);
!!PageTail() == true
<head == NULL dereferencing>
The race is pure theoretical. I don't it's possible to trigger it in
practice. But who knows.
We can fix the race by changing how encode PageTail() and compound_head()
within struct page to be able to update them in one shot.
The patch introduces page->compound_head into third double word block in
front of compound_dtor and compound_order. Bit 0 encodes PageTail() and
the rest bits are pointer to head page if bit zero is set.
The patch moves page->pmd_huge_pte out of word, just in case if an
architecture defines pgtable_t into something what can have the bit 0
set.
That means page->compound_head shares storage space with:
- page->lru.next;
- page->next;
- page->rcu_head.next;
That's too long list to be absolutely sure, but looks like nobody uses
bit 0 of the word.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
---
Documentation/vm/split_page_table_lock | 4 +-
arch/xtensa/configs/iss_defconfig | 1 -
include/linux/mm.h | 53 ++--------------------
include/linux/mm_types.h | 18 ++++++--
include/linux/page-flags.h | 80 ++++++++--------------------------
mm/Kconfig | 12 -----
mm/debug.c | 5 ---
mm/huge_memory.c | 3 +-
mm/hugetlb.c | 8 +---
mm/internal.h | 4 +-
mm/memory-failure.c | 7 ---
mm/page_alloc.c | 46 +++++++++++--------
mm/swap.c | 4 +-
13 files changed, 74 insertions(+), 171 deletions(-)
diff --git a/Documentation/vm/split_page_table_lock b/Documentation/vm/split_page_table_lock
index 6dea4fd5c961..62842a857dab 100644
--- a/Documentation/vm/split_page_table_lock
+++ b/Documentation/vm/split_page_table_lock
@@ -54,8 +54,8 @@ everything required is done by pgtable_page_ctor() and pgtable_page_dtor(),
which must be called on PTE table allocation / freeing.
Make sure the architecture doesn't use slab allocator for page table
-allocation: slab uses page->slab_cache and page->first_page for its pages.
-These fields share storage with page->ptl.
+allocation: slab uses page->slab_cache for its pages.
+This field shares storage with page->ptl.
PMD split lock only makes sense if you have more than two page table
levels.
diff --git a/arch/xtensa/configs/iss_defconfig b/arch/xtensa/configs/iss_defconfig
index e4d193e7a300..5c7c385f21c4 100644
--- a/arch/xtensa/configs/iss_defconfig
+++ b/arch/xtensa/configs/iss_defconfig
@@ -169,7 +169,6 @@ CONFIG_FLATMEM_MANUAL=y
# CONFIG_SPARSEMEM_MANUAL is not set
CONFIG_FLATMEM=y
CONFIG_FLAT_NODE_MEM_MAP=y
-CONFIG_PAGEFLAGS_EXTENDED=y
CONFIG_SPLIT_PTLOCK_CPUS=4
# CONFIG_PHYS_ADDR_T_64BIT is not set
CONFIG_ZONE_DMA_FLAG=1
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2cfe6051574c..9fc7dc8a49af 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -437,46 +437,6 @@ static inline void compound_unlock_irqrestore(struct page *page,
#endif
}
-static inline struct page *compound_head_by_tail(struct page *tail)
-{
- struct page *head = tail->first_page;
-
- /*
- * page->first_page may be a dangling pointer to an old
- * compound page, so recheck that it is still a tail
- * page before returning.
- */
- smp_rmb();
- if (likely(PageTail(tail)))
- return head;
- return tail;
-}
-
-/*
- * Since either compound page could be dismantled asynchronously in THP
- * or we access asynchronously arbitrary positioned struct page, there
- * would be tail flag race. To handle this race, we should call
- * smp_rmb() before checking tail flag. compound_head_by_tail() did it.
- */
-static inline struct page *compound_head(struct page *page)
-{
- if (unlikely(PageTail(page)))
- return compound_head_by_tail(page);
- return page;
-}
-
-/*
- * If we access compound page synchronously such as access to
- * allocated page, there is no need to handle tail flag race, so we can
- * check tail flag directly without any synchronization primitive.
- */
-static inline struct page *compound_head_fast(struct page *page)
-{
- if (unlikely(PageTail(page)))
- return page->first_page;
- return page;
-}
-
/*
* The atomic page->_mapcount, starts from -1: so that transitions
* both from it and to it can be tracked, using atomic_inc_and_test
@@ -525,7 +485,7 @@ static inline void get_huge_page_tail(struct page *page)
VM_BUG_ON_PAGE(!PageTail(page), page);
VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
VM_BUG_ON_PAGE(atomic_read(&page->_count) != 0, page);
- if (compound_tail_refcounted(page->first_page))
+ if (compound_tail_refcounted(compound_head(page)))
atomic_inc(&page->_mapcount);
}
@@ -548,13 +508,7 @@ static inline struct page *virt_to_head_page(const void *x)
{
struct page *page = virt_to_page(x);
- /*
- * We don't need to worry about synchronization of tail flag
- * when we call virt_to_head_page() since it is only called for
- * already allocated page and this page won't be freed until
- * this virt_to_head_page() is finished. So use _fast variant.
- */
- return compound_head_fast(page);
+ return compound_head(page);
}
/*
@@ -1496,8 +1450,7 @@ static inline bool ptlock_init(struct page *page)
* with 0. Make sure nobody took it in use in between.
*
* It can happen if arch try to use slab for page table allocation:
- * slab code uses page->slab_cache and page->first_page (for tail
- * pages), which share storage with page->ptl.
+ * slab code uses page->slab_cache, which share storage with page->ptl.
*/
VM_BUG_ON_PAGE(*(unsigned long *)&page->ptl, page);
if (!ptlock_alloc(page))
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 408a54563f65..ecaf3b1d0216 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -120,7 +120,13 @@ struct page {
};
};
- /* Third double word block */
+ /*
+ * Third double word block
+ *
+ * WARNING: bit 0 of the first word encode PageTail(). That means
+ * the rest users of the storage space MUST NOT use the bit to
+ * avoid collision and false-positive PageTail().
+ */
union {
struct list_head lru; /* Pageout list, eg. active_list
* protected by zone->lru_lock !
@@ -143,12 +149,19 @@ struct page {
*/
/* First tail page of compound page */
struct {
+ unsigned long compound_head; /* If bit zero is set */
unsigned short int compound_dtor;
unsigned short int compound_order;
};
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
- pgtable_t pmd_huge_pte; /* protected by page->ptl */
+ struct {
+ unsigned long __pad; /* do not overlay pmd_huge_pte
+ * with compound_head to avoid
+ * possible bit 0 collision.
+ */
+ pgtable_t pmd_huge_pte; /* protected by page->ptl */
+ };
#endif
};
@@ -169,7 +182,6 @@ struct page {
#endif
#endif
struct kmem_cache *slab_cache; /* SL[AU]B: Pointer to slab */
- struct page *first_page; /* Compound tail pages */
};
#ifdef CONFIG_MEMCG
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 41c93844fb1d..9b865158e452 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -86,12 +86,7 @@ enum pageflags {
PG_private, /* If pagecache, has fs-private data */
PG_private_2, /* If pagecache, has fs aux data */
PG_writeback, /* Page is under writeback */
-#ifdef CONFIG_PAGEFLAGS_EXTENDED
PG_head, /* A head page */
- PG_tail, /* A tail page */
-#else
- PG_compound, /* A compound page */
-#endif
PG_swapcache, /* Swap page: swp_entry_t in private */
PG_mappedtodisk, /* Has blocks allocated on-disk */
PG_reclaim, /* To be reclaimed asap */
@@ -387,85 +382,46 @@ static inline void set_page_writeback_keepwrite(struct page *page)
test_set_page_writeback_keepwrite(page);
}
-#ifdef CONFIG_PAGEFLAGS_EXTENDED
-/*
- * System with lots of page flags available. This allows separate
- * flags for PageHead() and PageTail() checks of compound pages so that bit
- * tests can be used in performance sensitive paths. PageCompound is
- * generally not used in hot code paths except arch/powerpc/mm/init_64.c
- * and arch/powerpc/kvm/book3s_64_vio_hv.c which use it to detect huge pages
- * and avoid handling those in real mode.
- */
__PAGEFLAG(Head, head) CLEARPAGEFLAG(Head, head)
-__PAGEFLAG(Tail, tail)
-static inline int PageCompound(struct page *page)
-{
- return page->flags & ((1L << PG_head) | (1L << PG_tail));
-
-}
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-static inline void ClearPageCompound(struct page *page)
+static inline int PageTail(struct page *page)
{
- BUG_ON(!PageHead(page));
- ClearPageHead(page);
+ return READ_ONCE(page->compound_head) & 1;
}
-#endif
-
-#define PG_head_mask ((1L << PG_head))
-#else
-/*
- * Reduce page flag use as much as possible by overlapping
- * compound page flags with the flags used for page cache pages. Possible
- * because PageCompound is always set for compound pages and not for
- * pages on the LRU and/or pagecache.
- */
-TESTPAGEFLAG(Compound, compound)
-__SETPAGEFLAG(Head, compound) __CLEARPAGEFLAG(Head, compound)
-
-/*
- * PG_reclaim is used in combination with PG_compound to mark the
- * head and tail of a compound page. This saves one page flag
- * but makes it impossible to use compound pages for the page cache.
- * The PG_reclaim bit would have to be used for reclaim or readahead
- * if compound pages enter the page cache.
- *
- * PG_compound & PG_reclaim => Tail page
- * PG_compound & ~PG_reclaim => Head page
- */
-#define PG_head_mask ((1L << PG_compound))
-#define PG_head_tail_mask ((1L << PG_compound) | (1L << PG_reclaim))
-
-static inline int PageHead(struct page *page)
+static inline void set_compound_head(struct page *page, struct page *head)
{
- return ((page->flags & PG_head_tail_mask) == PG_head_mask);
+ WRITE_ONCE(page->compound_head, (unsigned long)head + 1);
}
-static inline int PageTail(struct page *page)
+static inline void clear_compound_head(struct page *page)
{
- return ((page->flags & PG_head_tail_mask) == PG_head_tail_mask);
+ WRITE_ONCE(page->compound_head, 0);
}
-static inline void __SetPageTail(struct page *page)
+static inline struct page *compound_head(struct page *page)
{
- page->flags |= PG_head_tail_mask;
+ unsigned long head = READ_ONCE(page->compound_head);
+
+ if (unlikely(head & 1))
+ return (struct page *) (head - 1);
+ return page;
}
-static inline void __ClearPageTail(struct page *page)
+static inline int PageCompound(struct page *page)
{
- page->flags &= ~PG_head_tail_mask;
-}
+ return PageHead(page) || PageTail(page);
+}
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
static inline void ClearPageCompound(struct page *page)
{
- BUG_ON((page->flags & PG_head_tail_mask) != (1 << PG_compound));
- clear_bit(PG_compound, &page->flags);
+ BUG_ON(!PageHead(page));
+ ClearPageHead(page);
}
#endif
-#endif /* !PAGEFLAGS_EXTENDED */
+#define PG_head_mask ((1L << PG_head))
#ifdef CONFIG_HUGETLB_PAGE
int PageHuge(struct page *page);
diff --git a/mm/Kconfig b/mm/Kconfig
index e79de2bd12cd..454579d31081 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -200,18 +200,6 @@ config MEMORY_HOTREMOVE
depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
depends on MIGRATION
-#
-# If we have space for more page flags then we can enable additional
-# optimizations and functionality.
-#
-# Regular Sparsemem takes page flag bits for the sectionid if it does not
-# use a virtual memmap. Disable extended page flags for 32 bit platforms
-# that require the use of a sectionid in the page flags.
-#
-config PAGEFLAGS_EXTENDED
- def_bool y
- depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM
-
# Heavily threaded applications may benefit from splitting the mm-wide
# page_table_lock, so that faults on different parts of the user address
# space can be handled with less contention: split it at this NR_CPUS.
diff --git a/mm/debug.c b/mm/debug.c
index 76089ddf99ea..205e5ef957ab 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -25,12 +25,7 @@ static const struct trace_print_flags pageflag_names[] = {
{1UL << PG_private, "private" },
{1UL << PG_private_2, "private_2" },
{1UL << PG_writeback, "writeback" },
-#ifdef CONFIG_PAGEFLAGS_EXTENDED
{1UL << PG_head, "head" },
- {1UL << PG_tail, "tail" },
-#else
- {1UL << PG_compound, "compound" },
-#endif
{1UL << PG_swapcache, "swapcache" },
{1UL << PG_mappedtodisk, "mappedtodisk" },
{1UL << PG_reclaim, "reclaim" },
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 097c7a4bfbd9..330377f83ac7 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1686,8 +1686,7 @@ static void __split_huge_page_refcount(struct page *page,
(1L << PG_unevictable)));
page_tail->flags |= (1L << PG_dirty);
- /* clear PageTail before overwriting first_page */
- smp_wmb();
+ clear_compound_head(page_tail);
/*
* __split_huge_page_splitting() already set the
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8ea74caa1fa8..53c0709fd87b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -824,9 +824,8 @@ static void destroy_compound_gigantic_page(struct page *page,
struct page *p = page + 1;
for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
- __ClearPageTail(p);
+ clear_compound_head(p);
set_page_refcounted(p);
- p->first_page = NULL;
}
set_compound_order(page, 0);
@@ -1099,10 +1098,7 @@ static void prep_compound_gigantic_page(struct page *page, unsigned long order)
*/
__ClearPageReserved(p);
set_page_count(p, 0);
- p->first_page = page;
- /* Make sure p->first_page is always valid for PageTail() */
- smp_wmb();
- __SetPageTail(p);
+ set_compound_head(p, page);
}
}
diff --git a/mm/internal.h b/mm/internal.h
index 36b23f1e2ca6..89e21a07080a 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -61,9 +61,9 @@ static inline void __get_page_tail_foll(struct page *page,
* speculative page access (like in
* page_cache_get_speculative()) on tail pages.
*/
- VM_BUG_ON_PAGE(atomic_read(&page->first_page->_count) <= 0, page);
+ VM_BUG_ON_PAGE(atomic_read(&compound_head(page)->_count) <= 0, page);
if (get_page_head)
- atomic_inc(&page->first_page->_count);
+ atomic_inc(&compound_head(page)->_count);
get_huge_page_tail(page);
}
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 1f4446a90cef..4d1a5de9653d 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -787,8 +787,6 @@ static int me_huge_page(struct page *p, unsigned long pfn)
#define lru (1UL << PG_lru)
#define swapbacked (1UL << PG_swapbacked)
#define head (1UL << PG_head)
-#define tail (1UL << PG_tail)
-#define compound (1UL << PG_compound)
#define slab (1UL << PG_slab)
#define reserved (1UL << PG_reserved)
@@ -811,12 +809,7 @@ static struct page_state {
*/
{ slab, slab, MF_MSG_SLAB, me_kernel },
-#ifdef CONFIG_PAGEFLAGS_EXTENDED
{ head, head, MF_MSG_HUGE, me_huge_page },
- { tail, tail, MF_MSG_HUGE, me_huge_page },
-#else
- { compound, compound, MF_MSG_HUGE, me_huge_page },
-#endif
{ sc|dirty, sc|dirty, MF_MSG_DIRTY_SWAPCACHE, me_swapcache_dirty },
{ sc|dirty, sc, MF_MSG_CLEAN_SWAPCACHE, me_swapcache_clean },
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c6733cc3cbce..a56ad53ff553 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -424,15 +424,15 @@ out:
/*
* Higher-order pages are called "compound pages". They are structured thusly:
*
- * The first PAGE_SIZE page is called the "head page".
+ * The first PAGE_SIZE page is called the "head page" and have PG_head set.
*
- * The remaining PAGE_SIZE pages are called "tail pages".
+ * The remaining PAGE_SIZE pages are called "tail pages". PageTail() is encoded
+ * in bit 0 of page->compound_head. The rest of bits is pointer to head page.
*
- * All pages have PG_compound set. All tail pages have their ->first_page
- * pointing at the head page.
+ * The first tail page's ->compound_dtor holds the offset in array of compound
+ * page destructors. See compound_page_dtors.
*
- * The first tail page's ->lru.next holds the address of the compound page's
- * put_page() function. Its ->lru.prev holds the order of allocation.
+ * The first tail page's ->compound_order holds the order of allocation.
* This usage means that zero-order pages may not be compound.
*/
@@ -452,10 +452,7 @@ void prep_compound_page(struct page *page, unsigned long order)
for (i = 1; i < nr_pages; i++) {
struct page *p = page + i;
set_page_count(p, 0);
- p->first_page = page;
- /* Make sure p->first_page is always valid for PageTail() */
- smp_wmb();
- __SetPageTail(p);
+ set_compound_head(p, page);
}
}
@@ -830,17 +827,30 @@ static void free_one_page(struct zone *zone,
static int free_tail_pages_check(struct page *head_page, struct page *page)
{
- if (!IS_ENABLED(CONFIG_DEBUG_VM))
- return 0;
+ int ret = 1;
+
+ /*
+ * We rely page->lru.next never has bit 0 set, unless the page
+ * is PageTail(). Let's make sure that's true even for poisoned ->lru.
+ */
+ BUILD_BUG_ON((unsigned long)LIST_POISON1 & 1);
+
+ if (!IS_ENABLED(CONFIG_DEBUG_VM)) {
+ ret = 0;
+ goto out;
+ }
if (unlikely(!PageTail(page))) {
bad_page(page, "PageTail not set", 0);
- return 1;
+ goto out;
}
- if (unlikely(page->first_page != head_page)) {
- bad_page(page, "first_page not consistent", 0);
- return 1;
+ if (unlikely(compound_head(page) != head_page)) {
+ bad_page(page, "compound_head not consistent", 0);
+ goto out;
}
- return 0;
+ ret = 0;
+out:
+ clear_compound_head(page);
+ return ret;
}
static void __meminit __init_single_page(struct page *page, unsigned long pfn,
@@ -888,6 +898,8 @@ static void init_reserved_page(unsigned long pfn)
#else
static inline void init_reserved_page(unsigned long pfn)
{
+ /* Avoid false-positive PageTail() */
+ INIT_LIST_HEAD(&pfn_to_page(pfn)->lru);
}
#endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
diff --git a/mm/swap.c b/mm/swap.c
index a3a0a2f1f7c3..faa9e1687dea 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -200,7 +200,7 @@ out_put_single:
__put_single_page(page);
return;
}
- VM_BUG_ON_PAGE(page_head != page->first_page, page);
+ VM_BUG_ON_PAGE(page_head != compound_head(page), page);
/*
* We can release the refcount taken by
* get_page_unless_zero() now that
@@ -261,7 +261,7 @@ static void put_compound_page(struct page *page)
* Case 3 is possible, as we may race with
* __split_huge_page_refcount tearing down a THP page.
*/
- page_head = compound_head_by_tail(page);
+ page_head = compound_head(page);
if (!__compound_tail_refcounted(page_head))
put_unrefcounted_compound_page(page_head, page);
else
--
2.5.0
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^ permalink raw reply related [flat|nested] 11+ messages in thread* Re: [PATCHv4 5/7] mm: make compound_head() robust
2015-08-27 13:59 ` [PATCHv4 5/7] mm: make compound_head() robust Kirill A. Shutemov
@ 2015-08-27 15:21 ` Michal Hocko
0 siblings, 0 replies; 11+ messages in thread
From: Michal Hocko @ 2015-08-27 15:21 UTC (permalink / raw)
To: Kirill A. Shutemov
Cc: Andrew Morton, Hugh Dickins, Andrea Arcangeli, Dave Hansen,
Vlastimil Babka, Johannes Weiner, David Rientjes, linux-kernel,
linux-mm, Paul E. McKenney
On Thu 27-08-15 16:59:19, Kirill A. Shutemov wrote:
> Hugh has pointed that compound_head() call can be unsafe in some
> context. There's one example:
>
> CPU0 CPU1
>
> isolate_migratepages_block()
> page_count()
> compound_head()
> !!PageTail() == true
> put_page()
> tail->first_page = NULL
> head = tail->first_page
> alloc_pages(__GFP_COMP)
> prep_compound_page()
> tail->first_page = head
> __SetPageTail(p);
> !!PageTail() == true
> <head == NULL dereferencing>
>
> The race is pure theoretical. I don't it's possible to trigger it in
> practice. But who knows.
>
> We can fix the race by changing how encode PageTail() and compound_head()
> within struct page to be able to update them in one shot.
>
> The patch introduces page->compound_head into third double word block in
> front of compound_dtor and compound_order. Bit 0 encodes PageTail() and
> the rest bits are pointer to head page if bit zero is set.
>
> The patch moves page->pmd_huge_pte out of word, just in case if an
> architecture defines pgtable_t into something what can have the bit 0
> set.
This is a good idea.
> That means page->compound_head shares storage space with:
>
> - page->lru.next;
> - page->next;
> - page->rcu_head.next;
>
> That's too long list to be absolutely sure, but looks like nobody uses
> bit 0 of the word.
Let's see if we can make RCU to use a different bit here for its future
potential use.
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> ---
> Documentation/vm/split_page_table_lock | 4 +-
> arch/xtensa/configs/iss_defconfig | 1 -
> include/linux/mm.h | 53 ++--------------------
> include/linux/mm_types.h | 18 ++++++--
> include/linux/page-flags.h | 80 ++++++++--------------------------
> mm/Kconfig | 12 -----
> mm/debug.c | 5 ---
> mm/huge_memory.c | 3 +-
> mm/hugetlb.c | 8 +---
> mm/internal.h | 4 +-
> mm/memory-failure.c | 7 ---
> mm/page_alloc.c | 46 +++++++++++--------
> mm/swap.c | 4 +-
> 13 files changed, 74 insertions(+), 171 deletions(-)
>
> diff --git a/Documentation/vm/split_page_table_lock b/Documentation/vm/split_page_table_lock
> index 6dea4fd5c961..62842a857dab 100644
> --- a/Documentation/vm/split_page_table_lock
> +++ b/Documentation/vm/split_page_table_lock
> @@ -54,8 +54,8 @@ everything required is done by pgtable_page_ctor() and pgtable_page_dtor(),
> which must be called on PTE table allocation / freeing.
>
> Make sure the architecture doesn't use slab allocator for page table
> -allocation: slab uses page->slab_cache and page->first_page for its pages.
> -These fields share storage with page->ptl.
> +allocation: slab uses page->slab_cache for its pages.
> +This field shares storage with page->ptl.
>
> PMD split lock only makes sense if you have more than two page table
> levels.
> diff --git a/arch/xtensa/configs/iss_defconfig b/arch/xtensa/configs/iss_defconfig
> index e4d193e7a300..5c7c385f21c4 100644
> --- a/arch/xtensa/configs/iss_defconfig
> +++ b/arch/xtensa/configs/iss_defconfig
> @@ -169,7 +169,6 @@ CONFIG_FLATMEM_MANUAL=y
> # CONFIG_SPARSEMEM_MANUAL is not set
> CONFIG_FLATMEM=y
> CONFIG_FLAT_NODE_MEM_MAP=y
> -CONFIG_PAGEFLAGS_EXTENDED=y
> CONFIG_SPLIT_PTLOCK_CPUS=4
> # CONFIG_PHYS_ADDR_T_64BIT is not set
> CONFIG_ZONE_DMA_FLAG=1
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 2cfe6051574c..9fc7dc8a49af 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -437,46 +437,6 @@ static inline void compound_unlock_irqrestore(struct page *page,
> #endif
> }
>
> -static inline struct page *compound_head_by_tail(struct page *tail)
> -{
> - struct page *head = tail->first_page;
> -
> - /*
> - * page->first_page may be a dangling pointer to an old
> - * compound page, so recheck that it is still a tail
> - * page before returning.
> - */
> - smp_rmb();
> - if (likely(PageTail(tail)))
> - return head;
> - return tail;
> -}
> -
> -/*
> - * Since either compound page could be dismantled asynchronously in THP
> - * or we access asynchronously arbitrary positioned struct page, there
> - * would be tail flag race. To handle this race, we should call
> - * smp_rmb() before checking tail flag. compound_head_by_tail() did it.
> - */
> -static inline struct page *compound_head(struct page *page)
> -{
> - if (unlikely(PageTail(page)))
> - return compound_head_by_tail(page);
> - return page;
> -}
> -
> -/*
> - * If we access compound page synchronously such as access to
> - * allocated page, there is no need to handle tail flag race, so we can
> - * check tail flag directly without any synchronization primitive.
> - */
> -static inline struct page *compound_head_fast(struct page *page)
> -{
> - if (unlikely(PageTail(page)))
> - return page->first_page;
> - return page;
> -}
> -
> /*
> * The atomic page->_mapcount, starts from -1: so that transitions
> * both from it and to it can be tracked, using atomic_inc_and_test
> @@ -525,7 +485,7 @@ static inline void get_huge_page_tail(struct page *page)
> VM_BUG_ON_PAGE(!PageTail(page), page);
> VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
> VM_BUG_ON_PAGE(atomic_read(&page->_count) != 0, page);
> - if (compound_tail_refcounted(page->first_page))
> + if (compound_tail_refcounted(compound_head(page)))
> atomic_inc(&page->_mapcount);
> }
>
> @@ -548,13 +508,7 @@ static inline struct page *virt_to_head_page(const void *x)
> {
> struct page *page = virt_to_page(x);
>
> - /*
> - * We don't need to worry about synchronization of tail flag
> - * when we call virt_to_head_page() since it is only called for
> - * already allocated page and this page won't be freed until
> - * this virt_to_head_page() is finished. So use _fast variant.
> - */
> - return compound_head_fast(page);
> + return compound_head(page);
> }
>
> /*
> @@ -1496,8 +1450,7 @@ static inline bool ptlock_init(struct page *page)
> * with 0. Make sure nobody took it in use in between.
> *
> * It can happen if arch try to use slab for page table allocation:
> - * slab code uses page->slab_cache and page->first_page (for tail
> - * pages), which share storage with page->ptl.
> + * slab code uses page->slab_cache, which share storage with page->ptl.
> */
> VM_BUG_ON_PAGE(*(unsigned long *)&page->ptl, page);
> if (!ptlock_alloc(page))
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 408a54563f65..ecaf3b1d0216 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -120,7 +120,13 @@ struct page {
> };
> };
>
> - /* Third double word block */
> + /*
> + * Third double word block
> + *
> + * WARNING: bit 0 of the first word encode PageTail(). That means
> + * the rest users of the storage space MUST NOT use the bit to
> + * avoid collision and false-positive PageTail().
> + */
> union {
> struct list_head lru; /* Pageout list, eg. active_list
> * protected by zone->lru_lock !
> @@ -143,12 +149,19 @@ struct page {
> */
> /* First tail page of compound page */
> struct {
> + unsigned long compound_head; /* If bit zero is set */
> unsigned short int compound_dtor;
> unsigned short int compound_order;
> };
>
> #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
> - pgtable_t pmd_huge_pte; /* protected by page->ptl */
> + struct {
> + unsigned long __pad; /* do not overlay pmd_huge_pte
> + * with compound_head to avoid
> + * possible bit 0 collision.
> + */
> + pgtable_t pmd_huge_pte; /* protected by page->ptl */
> + };
> #endif
> };
>
> @@ -169,7 +182,6 @@ struct page {
> #endif
> #endif
> struct kmem_cache *slab_cache; /* SL[AU]B: Pointer to slab */
> - struct page *first_page; /* Compound tail pages */
> };
>
> #ifdef CONFIG_MEMCG
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 41c93844fb1d..9b865158e452 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -86,12 +86,7 @@ enum pageflags {
> PG_private, /* If pagecache, has fs-private data */
> PG_private_2, /* If pagecache, has fs aux data */
> PG_writeback, /* Page is under writeback */
> -#ifdef CONFIG_PAGEFLAGS_EXTENDED
> PG_head, /* A head page */
> - PG_tail, /* A tail page */
> -#else
> - PG_compound, /* A compound page */
> -#endif
> PG_swapcache, /* Swap page: swp_entry_t in private */
> PG_mappedtodisk, /* Has blocks allocated on-disk */
> PG_reclaim, /* To be reclaimed asap */
> @@ -387,85 +382,46 @@ static inline void set_page_writeback_keepwrite(struct page *page)
> test_set_page_writeback_keepwrite(page);
> }
>
> -#ifdef CONFIG_PAGEFLAGS_EXTENDED
> -/*
> - * System with lots of page flags available. This allows separate
> - * flags for PageHead() and PageTail() checks of compound pages so that bit
> - * tests can be used in performance sensitive paths. PageCompound is
> - * generally not used in hot code paths except arch/powerpc/mm/init_64.c
> - * and arch/powerpc/kvm/book3s_64_vio_hv.c which use it to detect huge pages
> - * and avoid handling those in real mode.
> - */
> __PAGEFLAG(Head, head) CLEARPAGEFLAG(Head, head)
> -__PAGEFLAG(Tail, tail)
>
> -static inline int PageCompound(struct page *page)
> -{
> - return page->flags & ((1L << PG_head) | (1L << PG_tail));
> -
> -}
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -static inline void ClearPageCompound(struct page *page)
> +static inline int PageTail(struct page *page)
> {
> - BUG_ON(!PageHead(page));
> - ClearPageHead(page);
> + return READ_ONCE(page->compound_head) & 1;
> }
> -#endif
> -
> -#define PG_head_mask ((1L << PG_head))
>
> -#else
> -/*
> - * Reduce page flag use as much as possible by overlapping
> - * compound page flags with the flags used for page cache pages. Possible
> - * because PageCompound is always set for compound pages and not for
> - * pages on the LRU and/or pagecache.
> - */
> -TESTPAGEFLAG(Compound, compound)
> -__SETPAGEFLAG(Head, compound) __CLEARPAGEFLAG(Head, compound)
> -
> -/*
> - * PG_reclaim is used in combination with PG_compound to mark the
> - * head and tail of a compound page. This saves one page flag
> - * but makes it impossible to use compound pages for the page cache.
> - * The PG_reclaim bit would have to be used for reclaim or readahead
> - * if compound pages enter the page cache.
> - *
> - * PG_compound & PG_reclaim => Tail page
> - * PG_compound & ~PG_reclaim => Head page
> - */
> -#define PG_head_mask ((1L << PG_compound))
> -#define PG_head_tail_mask ((1L << PG_compound) | (1L << PG_reclaim))
> -
> -static inline int PageHead(struct page *page)
> +static inline void set_compound_head(struct page *page, struct page *head)
> {
> - return ((page->flags & PG_head_tail_mask) == PG_head_mask);
> + WRITE_ONCE(page->compound_head, (unsigned long)head + 1);
> }
>
> -static inline int PageTail(struct page *page)
> +static inline void clear_compound_head(struct page *page)
> {
> - return ((page->flags & PG_head_tail_mask) == PG_head_tail_mask);
> + WRITE_ONCE(page->compound_head, 0);
> }
>
> -static inline void __SetPageTail(struct page *page)
> +static inline struct page *compound_head(struct page *page)
> {
> - page->flags |= PG_head_tail_mask;
> + unsigned long head = READ_ONCE(page->compound_head);
> +
> + if (unlikely(head & 1))
> + return (struct page *) (head - 1);
> + return page;
> }
>
> -static inline void __ClearPageTail(struct page *page)
> +static inline int PageCompound(struct page *page)
> {
> - page->flags &= ~PG_head_tail_mask;
> -}
> + return PageHead(page) || PageTail(page);
>
> +}
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> static inline void ClearPageCompound(struct page *page)
> {
> - BUG_ON((page->flags & PG_head_tail_mask) != (1 << PG_compound));
> - clear_bit(PG_compound, &page->flags);
> + BUG_ON(!PageHead(page));
> + ClearPageHead(page);
> }
> #endif
>
> -#endif /* !PAGEFLAGS_EXTENDED */
> +#define PG_head_mask ((1L << PG_head))
>
> #ifdef CONFIG_HUGETLB_PAGE
> int PageHuge(struct page *page);
> diff --git a/mm/Kconfig b/mm/Kconfig
> index e79de2bd12cd..454579d31081 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -200,18 +200,6 @@ config MEMORY_HOTREMOVE
> depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
> depends on MIGRATION
>
> -#
> -# If we have space for more page flags then we can enable additional
> -# optimizations and functionality.
> -#
> -# Regular Sparsemem takes page flag bits for the sectionid if it does not
> -# use a virtual memmap. Disable extended page flags for 32 bit platforms
> -# that require the use of a sectionid in the page flags.
> -#
> -config PAGEFLAGS_EXTENDED
> - def_bool y
> - depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM
> -
> # Heavily threaded applications may benefit from splitting the mm-wide
> # page_table_lock, so that faults on different parts of the user address
> # space can be handled with less contention: split it at this NR_CPUS.
> diff --git a/mm/debug.c b/mm/debug.c
> index 76089ddf99ea..205e5ef957ab 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -25,12 +25,7 @@ static const struct trace_print_flags pageflag_names[] = {
> {1UL << PG_private, "private" },
> {1UL << PG_private_2, "private_2" },
> {1UL << PG_writeback, "writeback" },
> -#ifdef CONFIG_PAGEFLAGS_EXTENDED
> {1UL << PG_head, "head" },
> - {1UL << PG_tail, "tail" },
> -#else
> - {1UL << PG_compound, "compound" },
> -#endif
> {1UL << PG_swapcache, "swapcache" },
> {1UL << PG_mappedtodisk, "mappedtodisk" },
> {1UL << PG_reclaim, "reclaim" },
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 097c7a4bfbd9..330377f83ac7 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1686,8 +1686,7 @@ static void __split_huge_page_refcount(struct page *page,
> (1L << PG_unevictable)));
> page_tail->flags |= (1L << PG_dirty);
>
> - /* clear PageTail before overwriting first_page */
> - smp_wmb();
> + clear_compound_head(page_tail);
>
> /*
> * __split_huge_page_splitting() already set the
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 8ea74caa1fa8..53c0709fd87b 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -824,9 +824,8 @@ static void destroy_compound_gigantic_page(struct page *page,
> struct page *p = page + 1;
>
> for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
> - __ClearPageTail(p);
> + clear_compound_head(p);
> set_page_refcounted(p);
> - p->first_page = NULL;
> }
>
> set_compound_order(page, 0);
> @@ -1099,10 +1098,7 @@ static void prep_compound_gigantic_page(struct page *page, unsigned long order)
> */
> __ClearPageReserved(p);
> set_page_count(p, 0);
> - p->first_page = page;
> - /* Make sure p->first_page is always valid for PageTail() */
> - smp_wmb();
> - __SetPageTail(p);
> + set_compound_head(p, page);
> }
> }
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 36b23f1e2ca6..89e21a07080a 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -61,9 +61,9 @@ static inline void __get_page_tail_foll(struct page *page,
> * speculative page access (like in
> * page_cache_get_speculative()) on tail pages.
> */
> - VM_BUG_ON_PAGE(atomic_read(&page->first_page->_count) <= 0, page);
> + VM_BUG_ON_PAGE(atomic_read(&compound_head(page)->_count) <= 0, page);
> if (get_page_head)
> - atomic_inc(&page->first_page->_count);
> + atomic_inc(&compound_head(page)->_count);
> get_huge_page_tail(page);
> }
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 1f4446a90cef..4d1a5de9653d 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -787,8 +787,6 @@ static int me_huge_page(struct page *p, unsigned long pfn)
> #define lru (1UL << PG_lru)
> #define swapbacked (1UL << PG_swapbacked)
> #define head (1UL << PG_head)
> -#define tail (1UL << PG_tail)
> -#define compound (1UL << PG_compound)
> #define slab (1UL << PG_slab)
> #define reserved (1UL << PG_reserved)
>
> @@ -811,12 +809,7 @@ static struct page_state {
> */
> { slab, slab, MF_MSG_SLAB, me_kernel },
>
> -#ifdef CONFIG_PAGEFLAGS_EXTENDED
> { head, head, MF_MSG_HUGE, me_huge_page },
> - { tail, tail, MF_MSG_HUGE, me_huge_page },
> -#else
> - { compound, compound, MF_MSG_HUGE, me_huge_page },
> -#endif
>
> { sc|dirty, sc|dirty, MF_MSG_DIRTY_SWAPCACHE, me_swapcache_dirty },
> { sc|dirty, sc, MF_MSG_CLEAN_SWAPCACHE, me_swapcache_clean },
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c6733cc3cbce..a56ad53ff553 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -424,15 +424,15 @@ out:
> /*
> * Higher-order pages are called "compound pages". They are structured thusly:
> *
> - * The first PAGE_SIZE page is called the "head page".
> + * The first PAGE_SIZE page is called the "head page" and have PG_head set.
> *
> - * The remaining PAGE_SIZE pages are called "tail pages".
> + * The remaining PAGE_SIZE pages are called "tail pages". PageTail() is encoded
> + * in bit 0 of page->compound_head. The rest of bits is pointer to head page.
> *
> - * All pages have PG_compound set. All tail pages have their ->first_page
> - * pointing at the head page.
> + * The first tail page's ->compound_dtor holds the offset in array of compound
> + * page destructors. See compound_page_dtors.
> *
> - * The first tail page's ->lru.next holds the address of the compound page's
> - * put_page() function. Its ->lru.prev holds the order of allocation.
> + * The first tail page's ->compound_order holds the order of allocation.
> * This usage means that zero-order pages may not be compound.
> */
>
> @@ -452,10 +452,7 @@ void prep_compound_page(struct page *page, unsigned long order)
> for (i = 1; i < nr_pages; i++) {
> struct page *p = page + i;
> set_page_count(p, 0);
> - p->first_page = page;
> - /* Make sure p->first_page is always valid for PageTail() */
> - smp_wmb();
> - __SetPageTail(p);
> + set_compound_head(p, page);
> }
> }
>
> @@ -830,17 +827,30 @@ static void free_one_page(struct zone *zone,
>
> static int free_tail_pages_check(struct page *head_page, struct page *page)
> {
> - if (!IS_ENABLED(CONFIG_DEBUG_VM))
> - return 0;
> + int ret = 1;
> +
> + /*
> + * We rely page->lru.next never has bit 0 set, unless the page
> + * is PageTail(). Let's make sure that's true even for poisoned ->lru.
> + */
> + BUILD_BUG_ON((unsigned long)LIST_POISON1 & 1);
> +
> + if (!IS_ENABLED(CONFIG_DEBUG_VM)) {
> + ret = 0;
> + goto out;
> + }
> if (unlikely(!PageTail(page))) {
> bad_page(page, "PageTail not set", 0);
> - return 1;
> + goto out;
> }
> - if (unlikely(page->first_page != head_page)) {
> - bad_page(page, "first_page not consistent", 0);
> - return 1;
> + if (unlikely(compound_head(page) != head_page)) {
> + bad_page(page, "compound_head not consistent", 0);
> + goto out;
> }
> - return 0;
> + ret = 0;
> +out:
> + clear_compound_head(page);
> + return ret;
> }
>
> static void __meminit __init_single_page(struct page *page, unsigned long pfn,
> @@ -888,6 +898,8 @@ static void init_reserved_page(unsigned long pfn)
> #else
> static inline void init_reserved_page(unsigned long pfn)
> {
> + /* Avoid false-positive PageTail() */
> + INIT_LIST_HEAD(&pfn_to_page(pfn)->lru);
> }
> #endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
>
> diff --git a/mm/swap.c b/mm/swap.c
> index a3a0a2f1f7c3..faa9e1687dea 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -200,7 +200,7 @@ out_put_single:
> __put_single_page(page);
> return;
> }
> - VM_BUG_ON_PAGE(page_head != page->first_page, page);
> + VM_BUG_ON_PAGE(page_head != compound_head(page), page);
> /*
> * We can release the refcount taken by
> * get_page_unless_zero() now that
> @@ -261,7 +261,7 @@ static void put_compound_page(struct page *page)
> * Case 3 is possible, as we may race with
> * __split_huge_page_refcount tearing down a THP page.
> */
> - page_head = compound_head_by_tail(page);
> + page_head = compound_head(page);
> if (!__compound_tail_refcounted(page_head))
> put_unrefcounted_compound_page(page_head, page);
> else
> --
> 2.5.0
--
Michal Hocko
SUSE Labs
--
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^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCHv4 6/7] mm: use 'unsigned int' for page order
2015-08-27 13:59 [PATCHv4 0/7] Fix compound_head() race Kirill A. Shutemov
` (4 preceding siblings ...)
2015-08-27 13:59 ` [PATCHv4 5/7] mm: make compound_head() robust Kirill A. Shutemov
@ 2015-08-27 13:59 ` Kirill A. Shutemov
2015-08-27 13:59 ` [PATCHv4 7/7] mm: use 'unsigned int' for compound_dtor/compound_order on 64BIT Kirill A. Shutemov
6 siblings, 0 replies; 11+ messages in thread
From: Kirill A. Shutemov @ 2015-08-27 13:59 UTC (permalink / raw)
To: Andrew Morton, Hugh Dickins
Cc: Andrea Arcangeli, Dave Hansen, Vlastimil Babka, Johannes Weiner,
Michal Hocko, David Rientjes, linux-kernel, linux-mm,
Kirill A. Shutemov
Let's try to be consistent about data type of page order.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
include/linux/mm.h | 5 +++--
mm/hugetlb.c | 19 ++++++++++---------
mm/internal.h | 4 ++--
mm/page_alloc.c | 27 +++++++++++++++------------
4 files changed, 30 insertions(+), 25 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9fc7dc8a49af..00a78439f392 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -557,7 +557,7 @@ static inline compound_page_dtor *get_compound_page_dtor(struct page *page)
return compound_page_dtors[page[1].compound_dtor];
}
-static inline int compound_order(struct page *page)
+static inline unsigned int compound_order(struct page *page)
{
if (!PageHead(page))
return 0;
@@ -1718,7 +1718,8 @@ extern void si_meminfo(struct sysinfo * val);
extern void si_meminfo_node(struct sysinfo *val, int nid);
extern __printf(3, 4)
-void warn_alloc_failed(gfp_t gfp_mask, int order, const char *fmt, ...);
+void warn_alloc_failed(gfp_t gfp_mask, unsigned int order,
+ const char *fmt, ...);
extern void setup_per_cpu_pageset(void);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 53c0709fd87b..bf64bfebc473 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -817,7 +817,7 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
#if defined(CONFIG_CMA) && defined(CONFIG_X86_64)
static void destroy_compound_gigantic_page(struct page *page,
- unsigned long order)
+ unsigned int order)
{
int i;
int nr_pages = 1 << order;
@@ -832,7 +832,7 @@ static void destroy_compound_gigantic_page(struct page *page,
__ClearPageHead(page);
}
-static void free_gigantic_page(struct page *page, unsigned order)
+static void free_gigantic_page(struct page *page, unsigned int order)
{
free_contig_range(page_to_pfn(page), 1 << order);
}
@@ -876,7 +876,7 @@ static bool zone_spans_last_pfn(const struct zone *zone,
return zone_spans_pfn(zone, last_pfn);
}
-static struct page *alloc_gigantic_page(int nid, unsigned order)
+static struct page *alloc_gigantic_page(int nid, unsigned int order)
{
unsigned long nr_pages = 1 << order;
unsigned long ret, pfn, flags;
@@ -912,7 +912,7 @@ static struct page *alloc_gigantic_page(int nid, unsigned order)
}
static void prep_new_huge_page(struct hstate *h, struct page *page, int nid);
-static void prep_compound_gigantic_page(struct page *page, unsigned long order);
+static void prep_compound_gigantic_page(struct page *page, unsigned int order);
static struct page *alloc_fresh_gigantic_page_node(struct hstate *h, int nid)
{
@@ -945,9 +945,9 @@ static int alloc_fresh_gigantic_page(struct hstate *h,
static inline bool gigantic_page_supported(void) { return true; }
#else
static inline bool gigantic_page_supported(void) { return false; }
-static inline void free_gigantic_page(struct page *page, unsigned order) { }
+static inline void free_gigantic_page(struct page *page, unsigned int order) { }
static inline void destroy_compound_gigantic_page(struct page *page,
- unsigned long order) { }
+ unsigned int order) { }
static inline int alloc_fresh_gigantic_page(struct hstate *h,
nodemask_t *nodes_allowed) { return 0; }
#endif
@@ -1073,7 +1073,7 @@ static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
put_page(page); /* free it into the hugepage allocator */
}
-static void prep_compound_gigantic_page(struct page *page, unsigned long order)
+static void prep_compound_gigantic_page(struct page *page, unsigned int order)
{
int i;
int nr_pages = 1 << order;
@@ -1640,7 +1640,8 @@ found:
return 1;
}
-static void __init prep_compound_huge_page(struct page *page, int order)
+static void __init prep_compound_huge_page(struct page *page,
+ unsigned int order)
{
if (unlikely(order > (MAX_ORDER - 1)))
prep_compound_gigantic_page(page, order);
@@ -2351,7 +2352,7 @@ static int __init hugetlb_init(void)
module_init(hugetlb_init);
/* Should be called on processing a hugepagesz=... option */
-void __init hugetlb_add_hstate(unsigned order)
+void __init hugetlb_add_hstate(unsigned int order)
{
struct hstate *h;
unsigned long i;
diff --git a/mm/internal.h b/mm/internal.h
index 89e21a07080a..9a9fc497593f 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -157,7 +157,7 @@ __find_buddy_index(unsigned long page_idx, unsigned int order)
extern int __isolate_free_page(struct page *page, unsigned int order);
extern void __free_pages_bootmem(struct page *page, unsigned long pfn,
unsigned int order);
-extern void prep_compound_page(struct page *page, unsigned long order);
+extern void prep_compound_page(struct page *page, unsigned int order);
#ifdef CONFIG_MEMORY_FAILURE
extern bool is_free_buddy_page(struct page *page);
#endif
@@ -214,7 +214,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
* page cannot be allocated or merged in parallel. Alternatively, it must
* handle invalid values gracefully, and use page_order_unsafe() below.
*/
-static inline unsigned long page_order(struct page *page)
+static inline unsigned int page_order(struct page *page)
{
/* PageBuddy() must be checked by the caller */
return page_private(page);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a56ad53ff553..81cfaca6b9fe 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -163,7 +163,7 @@ bool pm_suspended_storage(void)
#endif /* CONFIG_PM_SLEEP */
#ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
-int pageblock_order __read_mostly;
+unsigned int pageblock_order __read_mostly;
#endif
static void __free_pages_ok(struct page *page, unsigned int order);
@@ -441,7 +441,7 @@ static void free_compound_page(struct page *page)
__free_pages_ok(page, compound_order(page));
}
-void prep_compound_page(struct page *page, unsigned long order)
+void prep_compound_page(struct page *page, unsigned int order)
{
int i;
int nr_pages = 1 << order;
@@ -641,7 +641,7 @@ static inline void __free_one_page(struct page *page,
unsigned long combined_idx;
unsigned long uninitialized_var(buddy_idx);
struct page *buddy;
- int max_order = MAX_ORDER;
+ unsigned int max_order = MAX_ORDER;
VM_BUG_ON(!zone_is_initialized(zone));
VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP, page);
@@ -1444,7 +1444,7 @@ int move_freepages(struct zone *zone,
int migratetype)
{
struct page *page;
- unsigned long order;
+ unsigned int order;
int pages_moved = 0;
#ifndef CONFIG_HOLES_IN_ZONE
@@ -1558,7 +1558,7 @@ static bool can_steal_fallback(unsigned int order, int start_mt)
static void steal_suitable_fallback(struct zone *zone, struct page *page,
int start_type)
{
- int current_order = page_order(page);
+ unsigned int current_order = page_order(page);
int pages;
/* Take ownership for orders >= pageblock_order */
@@ -2665,7 +2665,7 @@ static DEFINE_RATELIMIT_STATE(nopage_rs,
DEFAULT_RATELIMIT_INTERVAL,
DEFAULT_RATELIMIT_BURST);
-void warn_alloc_failed(gfp_t gfp_mask, int order, const char *fmt, ...)
+void warn_alloc_failed(gfp_t gfp_mask, unsigned int order, const char *fmt, ...)
{
unsigned int filter = SHOW_MEM_FILTER_NODES;
@@ -2699,7 +2699,7 @@ void warn_alloc_failed(gfp_t gfp_mask, int order, const char *fmt, ...)
va_end(args);
}
- pr_warn("%s: page allocation failure: order:%d, mode:0x%x\n",
+ pr_warn("%s: page allocation failure: order:%u, mode:0x%x\n",
current->comm, order, gfp_mask);
dump_stack();
@@ -3458,7 +3458,8 @@ void free_kmem_pages(unsigned long addr, unsigned int order)
}
}
-static void *make_alloc_exact(unsigned long addr, unsigned order, size_t size)
+static void *make_alloc_exact(unsigned long addr, unsigned int order,
+ size_t size)
{
if (addr) {
unsigned long alloc_end = addr + (PAGE_SIZE << order);
@@ -3510,7 +3511,7 @@ EXPORT_SYMBOL(alloc_pages_exact);
*/
void * __meminit alloc_pages_exact_nid(int nid, size_t size, gfp_t gfp_mask)
{
- unsigned order = get_order(size);
+ unsigned int order = get_order(size);
struct page *p = alloc_pages_node(nid, gfp_mask, order);
if (!p)
return NULL;
@@ -3812,7 +3813,8 @@ void show_free_areas(unsigned int filter)
}
for_each_populated_zone(zone) {
- unsigned long nr[MAX_ORDER], flags, order, total = 0;
+ unsigned int order;
+ unsigned long nr[MAX_ORDER], flags, total = 0;
unsigned char types[MAX_ORDER];
if (skip_free_areas_node(filter, zone_to_nid(zone)))
@@ -4161,7 +4163,7 @@ static void build_zonelists(pg_data_t *pgdat)
nodemask_t used_mask;
int local_node, prev_node;
struct zonelist *zonelist;
- int order = current_zonelist_order;
+ unsigned int order = current_zonelist_order;
/* initialize zonelists */
for (i = 0; i < MAX_ZONELISTS; i++) {
@@ -6826,7 +6828,8 @@ int alloc_contig_range(unsigned long start, unsigned long end,
unsigned migratetype)
{
unsigned long outer_start, outer_end;
- int ret = 0, order;
+ unsigned int order;
+ int ret = 0;
struct compact_control cc = {
.nr_migratepages = 0,
--
2.5.0
--
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^ permalink raw reply related [flat|nested] 11+ messages in thread* [PATCHv4 7/7] mm: use 'unsigned int' for compound_dtor/compound_order on 64BIT
2015-08-27 13:59 [PATCHv4 0/7] Fix compound_head() race Kirill A. Shutemov
` (5 preceding siblings ...)
2015-08-27 13:59 ` [PATCHv4 6/7] mm: use 'unsigned int' for page order Kirill A. Shutemov
@ 2015-08-27 13:59 ` Kirill A. Shutemov
2015-08-27 15:19 ` Michal Hocko
6 siblings, 1 reply; 11+ messages in thread
From: Kirill A. Shutemov @ 2015-08-27 13:59 UTC (permalink / raw)
To: Andrew Morton, Hugh Dickins
Cc: Andrea Arcangeli, Dave Hansen, Vlastimil Babka, Johannes Weiner,
Michal Hocko, David Rientjes, linux-kernel, linux-mm,
Kirill A. Shutemov
On 64 bit system we have enough space in struct page to encode
compound_dtor and compound_order with unsigned int.
On x86-64 it leads to slightly smaller code size due usesage of plain
MOV instead of MOVZX (zero-extended move) or similar effect.
allyesconfig:
text data bss dec hex filename
159520446 48146736 72196096 279863278 10ae5fee vmlinux.pre
159520382 48146736 72196096 279863214 10ae5fae vmlinux.post
On other architectures without native support of 16-bit data types the
difference can be bigger.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
include/linux/mm_types.h | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index ecaf3b1d0216..39b0db74ba5e 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -150,8 +150,13 @@ struct page {
/* First tail page of compound page */
struct {
unsigned long compound_head; /* If bit zero is set */
+#ifdef CONFIG_64BIT
+ unsigned int compound_dtor;
+ unsigned int compound_order;
+#else
unsigned short int compound_dtor;
unsigned short int compound_order;
+#endif
};
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
--
2.5.0
--
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^ permalink raw reply related [flat|nested] 11+ messages in thread* Re: [PATCHv4 7/7] mm: use 'unsigned int' for compound_dtor/compound_order on 64BIT
2015-08-27 13:59 ` [PATCHv4 7/7] mm: use 'unsigned int' for compound_dtor/compound_order on 64BIT Kirill A. Shutemov
@ 2015-08-27 15:19 ` Michal Hocko
0 siblings, 0 replies; 11+ messages in thread
From: Michal Hocko @ 2015-08-27 15:19 UTC (permalink / raw)
To: Kirill A. Shutemov
Cc: Andrew Morton, Hugh Dickins, Andrea Arcangeli, Dave Hansen,
Vlastimil Babka, Johannes Weiner, David Rientjes, linux-kernel,
linux-mm
On Thu 27-08-15 16:59:21, Kirill A. Shutemov wrote:
> On 64 bit system we have enough space in struct page to encode
> compound_dtor and compound_order with unsigned int.
>
> On x86-64 it leads to slightly smaller code size due usesage of plain
> MOV instead of MOVZX (zero-extended move) or similar effect.
>
> allyesconfig:
>
> text data bss dec hex filename
> 159520446 48146736 72196096 279863278 10ae5fee vmlinux.pre
> 159520382 48146736 72196096 279863214 10ae5fae vmlinux.post
64B is not much, really, but if that works as a microptimization then I
have no objections.
> On other architectures without native support of 16-bit data types the
> difference can be bigger.
Thank you for pulling this out of the original patch.
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
> ---
> include/linux/mm_types.h | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index ecaf3b1d0216..39b0db74ba5e 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -150,8 +150,13 @@ struct page {
> /* First tail page of compound page */
> struct {
> unsigned long compound_head; /* If bit zero is set */
> +#ifdef CONFIG_64BIT
> + unsigned int compound_dtor;
> + unsigned int compound_order;
> +#else
> unsigned short int compound_dtor;
> unsigned short int compound_order;
> +#endif
> };
>
> #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
> --
> 2.5.0
--
Michal Hocko
SUSE Labs
--
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^ permalink raw reply [flat|nested] 11+ messages in thread