[PATCH] mm: extend zero pages to same element pages for zram

From: zhouxianrong
Date: Fri Feb 03 2017 - 03:40:44 EST

From: zhouxianrong <zhouxianrong@xxxxxxxxxx>

test result as listed below:

zero pattern_char pattern_short pattern_int pattern_long total (unit)
162989 14454 3534 23516 2769 3294399 (page)

statistics for the result:

zero pattern_char pattern_short pattern_int pattern_long
AVERAGE 0.745696298 0.085937175 0.015957701 0.131874915 0.020533911
STDEV 0.035623777 0.016892402 0.004454534 0.021657123 0.019420072
MAX 0.973813421 0.222222222 0.021409518 0.211812245 0.176512625
MIN 0.645431905 0.004634398 0 0 0

Signed-off-by: zhouxianrong <zhouxianrong@xxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 122 ++++++++++++++++++++++++++++++++---------
drivers/block/zram/zram_drv.h | 11 ++--
2 files changed, 102 insertions(+), 31 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index e5ab7d9..e826d0d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -95,6 +95,17 @@ static void zram_clear_flag(struct zram_meta *meta, u32 index,
meta->table[index].value &= ~BIT(flag);
}

+static inline void zram_set_element(struct zram_meta *meta, u32 index,
+ unsigned long element)
+{
+ meta->table[index].element = element;
+}
+
+static inline void zram_clear_element(struct zram_meta *meta, u32 index)
+{
+ meta->table[index].element = 0;
+}
+
static size_t zram_get_obj_size(struct zram_meta *meta, u32 index)
{
return meta->table[index].value & (BIT(ZRAM_FLAG_SHIFT) - 1);
@@ -167,31 +178,78 @@ static inline void update_used_max(struct zram *zram,
} while (old_max != cur_max);
}

-static bool page_zero_filled(void *ptr)
+static inline void zram_fill_page(char *ptr, unsigned long value)
+{
+ int i;
+ unsigned long *page = (unsigned long *)ptr;
+
+ if (likely(value == 0)) {
+ clear_page(ptr);
+ } else {
+ for (i = 0; i < PAGE_SIZE / sizeof(*page); i++)
+ page[i] = value;
+ }
+}
+
+static inline void zram_fill_page_partial(char *ptr, unsigned int size,
+ unsigned long value)
+{
+ int i;
+ unsigned long *page;
+
+ if (likely(value == 0)) {
+ memset(ptr, 0, size);
+ return;
+ }
+
+ i = ((unsigned long)ptr) % sizeof(*page);
+ if (i) {
+ while (i < sizeof(*page)) {
+ *ptr++ = (value >> (i * 8)) & 0xff;
+ --size;
+ ++i;
+ }
+ }
+
+ for (i = size / sizeof(*page); i > 0; --i) {
+ page = (unsigned long *)ptr;
+ *page = value;
+ ptr += sizeof(*page);
+ size -= sizeof(*page);
+ }
+
+ for (i = 0; i < size; ++i)
+ *ptr++ = (value >> (i * 8)) & 0xff;
+}
+
+static bool page_same_filled(void *ptr, unsigned long *element)
{
unsigned int pos;
unsigned long *page;

page = (unsigned long *)ptr;

- for (pos = 0; pos != PAGE_SIZE / sizeof(*page); pos++) {
- if (page[pos])
+ for (pos = 0; pos < PAGE_SIZE / sizeof(*page) - 1; pos++) {
+ if (page[pos] != page[pos + 1])
return false;
}

+ *element = page[pos];
+
return true;
}

-static void handle_zero_page(struct bio_vec *bvec)
+static void handle_same_page(struct bio_vec *bvec, unsigned long element)
{
struct page *page = bvec->bv_page;
void *user_mem;

user_mem = kmap_atomic(page);
if (is_partial_io(bvec))
- memset(user_mem + bvec->bv_offset, 0, bvec->bv_len);
+ zram_fill_page_partial(user_mem + bvec->bv_offset, bvec->bv_len,
+ element);
else
- clear_page(user_mem);
+ zram_fill_page(user_mem, element);
kunmap_atomic(user_mem);

flush_dcache_page(page);
@@ -440,7 +498,7 @@ static ssize_t mm_stat_show(struct device *dev,
mem_used << PAGE_SHIFT,
zram->limit_pages << PAGE_SHIFT,
max_used << PAGE_SHIFT,
- (u64)atomic64_read(&zram->stats.zero_pages),
+ (u64)atomic64_read(&zram->stats.same_pages),
pool_stats.pages_compacted);
up_read(&zram->init_lock);

@@ -473,7 +531,7 @@ static ssize_t debug_stat_show(struct device *dev,
ZRAM_ATTR_RO(failed_writes);
ZRAM_ATTR_RO(invalid_io);
ZRAM_ATTR_RO(notify_free);
-ZRAM_ATTR_RO(zero_pages);
+ZRAM_ATTR_RO(same_pages);
ZRAM_ATTR_RO(compr_data_size);

static inline bool zram_meta_get(struct zram *zram)
@@ -495,11 +553,17 @@ static void zram_meta_free(struct zram_meta *meta, u64 disksize)

/* Free all pages that are still in this zram device */
for (index = 0; index < num_pages; index++) {
- unsigned long handle = meta->table[index].handle;
+ unsigned long handle;
+
+ bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
+ handle = meta->table[index].handle;

- if (!handle)
+ if (!handle || zram_test_flag(meta, index, ZRAM_SAME)) {
+ bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
continue;
+ }

+ bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
zs_free(meta->mem_pool, handle);
}

@@ -547,18 +611,20 @@ static void zram_free_page(struct zram *zram, size_t index)
struct zram_meta *meta = zram->meta;
unsigned long handle = meta->table[index].handle;

- if (unlikely(!handle)) {
- /*
- * No memory is allocated for zero filled pages.
- * Simply clear zero page flag.
- */
- if (zram_test_flag(meta, index, ZRAM_ZERO)) {
- zram_clear_flag(meta, index, ZRAM_ZERO);
- atomic64_dec(&zram->stats.zero_pages);
- }
+ /*
+ * No memory is allocated for same element filled pages.
+ * Simply clear same page flag.
+ */
+ if (zram_test_flag(meta, index, ZRAM_SAME)) {
+ zram_clear_flag(meta, index, ZRAM_SAME);
+ zram_clear_element(meta, index);
+ atomic64_dec(&zram->stats.same_pages);
return;
}

+ if (unlikely(!handle))
+ return;
+
zs_free(meta->mem_pool, handle);

atomic64_sub(zram_get_obj_size(meta, index),
@@ -581,9 +647,9 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
handle = meta->table[index].handle;
size = zram_get_obj_size(meta, index);

- if (!handle || zram_test_flag(meta, index, ZRAM_ZERO)) {
+ if (!handle || zram_test_flag(meta, index, ZRAM_SAME)) {
bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
- clear_page(mem);
+ zram_fill_page(mem, meta->table[index].element);
return 0;
}

@@ -619,9 +685,9 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,

bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
if (unlikely(!meta->table[index].handle) ||
- zram_test_flag(meta, index, ZRAM_ZERO)) {
+ zram_test_flag(meta, index, ZRAM_SAME)) {
bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
- handle_zero_page(bvec);
+ handle_same_page(bvec, meta->table[index].element);
return 0;
}
bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
@@ -669,6 +735,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
struct zram_meta *meta = zram->meta;
struct zcomp_strm *zstrm = NULL;
unsigned long alloced_pages;
+ unsigned long element;

page = bvec->bv_page;
if (is_partial_io(bvec)) {
@@ -697,16 +764,17 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
uncmem = user_mem;
}

- if (page_zero_filled(uncmem)) {
+ if (page_same_filled(uncmem, &element)) {
if (user_mem)
kunmap_atomic(user_mem);
/* Free memory associated with this sector now. */
bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
zram_free_page(zram, index);
- zram_set_flag(meta, index, ZRAM_ZERO);
+ zram_set_flag(meta, index, ZRAM_SAME);
+ zram_set_element(meta, index, element);
bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);

- atomic64_inc(&zram->stats.zero_pages);
+ atomic64_inc(&zram->stats.same_pages);
ret = 0;
goto out;
}
@@ -1206,7 +1274,7 @@ static int zram_open(struct block_device *bdev, fmode_t mode)
&dev_attr_compact.attr,
&dev_attr_invalid_io.attr,
&dev_attr_notify_free.attr,
- &dev_attr_zero_pages.attr,
+ &dev_attr_same_pages.attr,
&dev_attr_orig_data_size.attr,
&dev_attr_compr_data_size.attr,
&dev_attr_mem_used_total.attr,
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 74fcf10..4bb92e1 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -60,8 +60,8 @@

/* Flags for zram pages (table[page_no].value) */
enum zram_pageflags {
- /* Page consists entirely of zeros */
- ZRAM_ZERO = ZRAM_FLAG_SHIFT,
+ /* Page consists entirely of same elements */
+ ZRAM_SAME = ZRAM_FLAG_SHIFT,
ZRAM_ACCESS, /* page is now accessed */

__NR_ZRAM_PAGEFLAGS,
@@ -71,7 +71,10 @@ enum zram_pageflags {

/* Allocated for each disk page */
struct zram_table_entry {
- unsigned long handle;
+ union {
+ unsigned long handle;
+ unsigned long element;
+ };
unsigned long value;
};

@@ -83,7 +86,7 @@ struct zram_stats {
atomic64_t failed_writes; /* can happen when memory is too low */
atomic64_t invalid_io; /* non-page-aligned I/O requests */
atomic64_t notify_free; /* no. of swap slot free notifications */
- atomic64_t zero_pages; /* no. of zero filled pages */
+ atomic64_t same_pages; /* no. of same element filled pages */
atomic64_t pages_stored; /* no. of pages currently stored */
atomic_long_t max_used_pages; /* no. of maximum pages stored */
atomic64_t writestall; /* no. of write slow paths */
--
1.7.9.5