[PATCH v6 10/12] zsmalloc: use freeobj for index

From: Minchan Kim
Date: Fri May 20 2016 - 10:25:01 EST

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Zsmalloc stores first free object's <PFN, obj_idx> position into
freeobj in each zspage. If we change it with index from first_page
instead of position, it makes page migration simple because we
don't need to correct other entries for linked list if a page is
migrated out.

Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
mm/zsmalloc.c | 139 ++++++++++++++++++++++++++++++----------------------------
1 file changed, 73 insertions(+), 66 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 8fc16cc4d76d..a5da5edfc1d0 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -69,9 +69,7 @@
* Object location (<PFN>, <obj_idx>) is encoded as
* as single (unsigned long) handle value.
*
- * Note that object index <obj_idx> is relative to system
- * page <PFN> it is stored in, so for each sub-page belonging
- * to a zspage, obj_idx starts with 0.
+ * Note that object index <obj_idx> starts from 0.
*
* This is made more complicated by various memory models and PAE.
*/
@@ -212,10 +210,10 @@ struct size_class {
struct link_free {
union {
/*
- * Position of next free chunk (encodes <PFN, obj_idx>)
+ * Free object index;
* It's valid for non-allocated object
*/
- void *next;
+ unsigned long next;
/*
* Handle of allocated object.
*/
@@ -259,7 +257,7 @@ struct zspage {
unsigned int class:CLASS_BITS;
};
unsigned int inuse;
- void *freeobj;
+ unsigned int freeobj;
struct page *first_page;
struct list_head list; /* fullness list */
};
@@ -457,14 +455,14 @@ static inline void set_first_obj_offset(struct page *page, int offset)
page->index = offset;
}

-static inline unsigned long get_freeobj(struct zspage *zspage)
+static inline unsigned int get_freeobj(struct zspage *zspage)
{
- return (unsigned long)zspage->freeobj;
+ return zspage->freeobj;
}

-static inline void set_freeobj(struct zspage *zspage, unsigned long obj)
+static inline void set_freeobj(struct zspage *zspage, unsigned int obj)
{
- zspage->freeobj = (void *)obj;
+ zspage->freeobj = obj;
}

static void get_zspage_mapping(struct zspage *zspage,
@@ -806,6 +804,10 @@ static int get_pages_per_zspage(int class_size)
return max_usedpc_order;
}

+static struct page *get_first_page(struct zspage *zspage)
+{
+ return zspage->first_page;
+}

static struct zspage *get_zspage(struct page *page)
{
@@ -817,37 +819,33 @@ static struct page *get_next_page(struct page *page)
return page->next;
}

-/*
- * Encode <page, obj_idx> as a single handle value.
- * We use the least bit of handle for tagging.
+/**
+ * obj_to_location - get (<page>, <obj_idx>) from encoded object value
+ * @page: page object resides in zspage
+ * @obj_idx: object index
*/
-static void *location_to_obj(struct page *page, unsigned long obj_idx)
+static void obj_to_location(unsigned long obj, struct page **page,
+ unsigned int *obj_idx)
{
- unsigned long obj;
+ obj >>= OBJ_TAG_BITS;
+ *page = pfn_to_page(obj >> OBJ_INDEX_BITS);
+ *obj_idx = (obj & OBJ_INDEX_MASK);
+}

- if (!page) {
- VM_BUG_ON(obj_idx);
- return NULL;
- }
+/**
+ * location_to_obj - get obj value encoded from (<page>, <obj_idx>)
+ * @page: page object resides in zspage
+ * @obj_idx: object index
+ */
+static unsigned long location_to_obj(struct page *page, unsigned int obj_idx)
+{
+ unsigned long obj;

obj = page_to_pfn(page) << OBJ_INDEX_BITS;
- obj |= ((obj_idx) & OBJ_INDEX_MASK);
+ obj |= obj_idx & OBJ_INDEX_MASK;
obj <<= OBJ_TAG_BITS;

- return (void *)obj;
-}
-
-/*
- * Decode <page, obj_idx> pair from the given object handle. We adjust the
- * decoded obj_idx back to its original value since it was adjusted in
- * location_to_obj().
- */
-static void obj_to_location(unsigned long obj, struct page **page,
- unsigned long *obj_idx)
-{
- obj >>= OBJ_TAG_BITS;
- *page = pfn_to_page(obj >> OBJ_INDEX_BITS);
- *obj_idx = (obj & OBJ_INDEX_MASK);
+ return obj;
}

static unsigned long handle_to_obj(unsigned long handle)
@@ -865,16 +863,6 @@ static unsigned long obj_to_head(struct size_class *class, struct page *page,
return *(unsigned long *)obj;
}

-static unsigned long obj_idx_to_offset(struct page *page,
- unsigned long obj_idx, int class_size)
-{
- unsigned long off;
-
- off = get_first_obj_offset(page);
-
- return off + obj_idx * class_size;
-}
-
static inline int trypin_tag(unsigned long handle)
{
return bit_spin_trylock(HANDLE_PIN_BIT, (unsigned long *)handle);
@@ -918,13 +906,13 @@ static void free_zspage(struct zs_pool *pool, struct zspage *zspage)
/* Initialize a newly allocated zspage */
static void init_zspage(struct size_class *class, struct zspage *zspage)
{
+ unsigned int freeobj = 1;
unsigned long off = 0;
struct page *page = zspage->first_page;

while (page) {
struct page *next_page;
struct link_free *link;
- unsigned int i = 1;
void *vaddr;

set_first_obj_offset(page, off);
@@ -933,7 +921,7 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
link = (struct link_free *)vaddr + off / sizeof(*link);

while ((off += class->size) < PAGE_SIZE) {
- link->next = location_to_obj(page, i++);
+ link->next = freeobj++ << OBJ_ALLOCATED_TAG;
link += class->size / sizeof(*link);
}

@@ -943,14 +931,21 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
* page (if present)
*/
next_page = get_next_page(page);
- link->next = location_to_obj(next_page, 0);
+ if (next_page) {
+ link->next = freeobj++ << OBJ_ALLOCATED_TAG;
+ } else {
+ /*
+ * Reset OBJ_ALLOCATED_TAG bit to last link to tell
+ * whether it's allocated object or not.
+ */
+ link->next = -1 << OBJ_ALLOCATED_TAG;
+ }
kunmap_atomic(vaddr);
page = next_page;
off %= PAGE_SIZE;
}

- set_freeobj(zspage,
- (unsigned long)location_to_obj(zspage->first_page, 0));
+ set_freeobj(zspage, 0);
}

static void create_page_chain(struct zspage *zspage, struct page *pages[],
@@ -1267,7 +1262,8 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
{
struct zspage *zspage;
struct page *page;
- unsigned long obj, obj_idx, off;
+ unsigned long obj, off;
+ unsigned int obj_idx;

unsigned int class_idx;
enum fullness_group fg;
@@ -1291,7 +1287,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
zspage = get_zspage(page);
get_zspage_mapping(zspage, &class_idx, &fg);
class = pool->size_class[class_idx];
- off = obj_idx_to_offset(page, obj_idx, class->size);
+ off = (class->size * obj_idx) & ~PAGE_MASK;

area = &get_cpu_var(zs_map_area);
area->vm_mm = mm;
@@ -1320,7 +1316,8 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
{
struct zspage *zspage;
struct page *page;
- unsigned long obj, obj_idx, off;
+ unsigned long obj, off;
+ unsigned int obj_idx;

unsigned int class_idx;
enum fullness_group fg;
@@ -1332,7 +1329,7 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
zspage = get_zspage(page);
get_zspage_mapping(zspage, &class_idx, &fg);
class = pool->size_class[class_idx];
- off = obj_idx_to_offset(page, obj_idx, class->size);
+ off = (class->size * obj_idx) & ~PAGE_MASK;

area = this_cpu_ptr(&zs_map_area);
if (off + class->size <= PAGE_SIZE)
@@ -1354,21 +1351,28 @@ EXPORT_SYMBOL_GPL(zs_unmap_object);
static unsigned long obj_malloc(struct size_class *class,
struct zspage *zspage, unsigned long handle)
{
+ int i, nr_page, offset;
unsigned long obj;
struct link_free *link;

struct page *m_page;
- unsigned long m_objidx, m_offset;
+ unsigned long m_offset;
void *vaddr;

handle |= OBJ_ALLOCATED_TAG;
obj = get_freeobj(zspage);
- obj_to_location(obj, &m_page, &m_objidx);
- m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);
+
+ offset = obj * class->size;
+ nr_page = offset >> PAGE_SHIFT;
+ m_offset = offset & ~PAGE_MASK;
+ m_page = get_first_page(zspage);
+
+ for (i = 0; i < nr_page; i++)
+ m_page = get_next_page(m_page);

vaddr = kmap_atomic(m_page);
link = (struct link_free *)vaddr + m_offset / sizeof(*link);
- set_freeobj(zspage, (unsigned long)link->next);
+ set_freeobj(zspage, link->next >> OBJ_ALLOCATED_TAG);
if (!class->huge)
/* record handle in the header of allocated chunk */
link->handle = handle;
@@ -1380,6 +1384,8 @@ static unsigned long obj_malloc(struct size_class *class,
mod_zspage_inuse(zspage, 1);
zs_stat_inc(class, OBJ_USED, 1);

+ obj = location_to_obj(m_page, obj);
+
return obj;
}

@@ -1445,22 +1451,22 @@ static void obj_free(struct size_class *class, unsigned long obj)
struct link_free *link;
struct zspage *zspage;
struct page *f_page;
- unsigned long f_objidx, f_offset;
+ unsigned long f_offset;
+ unsigned int f_objidx;
void *vaddr;

obj &= ~OBJ_ALLOCATED_TAG;
obj_to_location(obj, &f_page, &f_objidx);
+ f_offset = (class->size * f_objidx) & ~PAGE_MASK;
zspage = get_zspage(f_page);

- f_offset = obj_idx_to_offset(f_page, f_objidx, class->size);
-
vaddr = kmap_atomic(f_page);

/* Insert this object in containing zspage's freelist */
link = (struct link_free *)(vaddr + f_offset);
- link->next = (void *)get_freeobj(zspage);
+ link->next = get_freeobj(zspage) << OBJ_ALLOCATED_TAG;
kunmap_atomic(vaddr);
- set_freeobj(zspage, obj);
+ set_freeobj(zspage, f_objidx);
mod_zspage_inuse(zspage, -1);
zs_stat_dec(class, OBJ_USED, 1);
}
@@ -1469,7 +1475,8 @@ void zs_free(struct zs_pool *pool, unsigned long handle)
{
struct zspage *zspage;
struct page *f_page;
- unsigned long obj, f_objidx;
+ unsigned long obj;
+ unsigned int f_objidx;
int class_idx;
struct size_class *class;
enum fullness_group fullness;
@@ -1506,7 +1513,7 @@ static void zs_object_copy(struct size_class *class, unsigned long dst,
unsigned long src)
{
struct page *s_page, *d_page;
- unsigned long s_objidx, d_objidx;
+ unsigned int s_objidx, d_objidx;
unsigned long s_off, d_off;
void *s_addr, *d_addr;
int s_size, d_size, size;
@@ -1517,8 +1524,8 @@ static void zs_object_copy(struct size_class *class, unsigned long dst,
obj_to_location(src, &s_page, &s_objidx);
obj_to_location(dst, &d_page, &d_objidx);

- s_off = obj_idx_to_offset(s_page, s_objidx, class->size);
- d_off = obj_idx_to_offset(d_page, d_objidx, class->size);
+ s_off = (class->size * s_objidx) & ~PAGE_MASK;
+ d_off = (class->size * d_objidx) & ~PAGE_MASK;

if (s_off + class->size > PAGE_SIZE)
s_size = PAGE_SIZE - s_off;
--
1.9.1

Next message: Vegard Nossum: "Re: [PATCH 3.12 69/76] net: fix infoleak in rtnetlink"
Previous message: Minchan Kim: "[PATCH v6 12/12] zram: use __GFP_MOVABLE for memory allocation"
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