[PATCH] mm: extend zero pages to same element pages for zram
From: zhouxianrong
Date: Fri Jan 13 2017 - 03:34:13 EST
From: zhouxianrong <zhouxianrong@xxxxxxxxxx>
the idea is that without doing more calculations we extend zero pages
to same element pages for zram. zero page is special case of
same element page with zero element.
1. the test is done under android 7.0
2. startup too many applications circularly
3. sample the zero pages, same pages (none-zero element)
and total pages in function page_zero_filled
the result is listed as below:
ZERO SAME TOTAL
36214 17842 598196
ZERO/TOTAL SAME/TOTAL (ZERO+SAME)/TOTAL ZERO/SAME
AVERAGE 0.060631909 0.024990816 0.085622726 2.663825038
STDEV 0.00674612 0.005887625 0.009707034 2.115881328
MAX 0.069698422 0.030046087 0.094975336 7.56043956
MIN 0.03959586 0.007332205 0.056055193 1.928985507
from above data, the benefit is about 2.5% and up to 3% of total
swapout pages.
the defect of the patch is that when we recovery a page from
non-zero element the operations are low efficient for partial
read.
Signed-off-by: zhouxianrong <zhouxianrong@xxxxxxxxxx>
---
Documentation/ABI/testing/sysfs-block-zram | 12 +--
Documentation/blockdev/zram.txt | 4 +-
drivers/block/zram/zram_drv.c | 110 +++++++++++++++++++++-------
drivers/block/zram/zram_drv.h | 11 ++-
4 files changed, 100 insertions(+), 37 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
index 4518d30..1a759fa 100644
--- a/Documentation/ABI/testing/sysfs-block-zram
+++ b/Documentation/ABI/testing/sysfs-block-zram
@@ -86,21 +86,21 @@ Description:
ones are sent by filesystem mounted with discard option,
whenever some data blocks are getting discarded.
-What: /sys/block/zram<id>/zero_pages
+What: /sys/block/zram<id>/same_pages
Date: August 2010
Contact: Nitin Gupta <ngupta@xxxxxxxxxx>
Description:
- The zero_pages file is read-only and specifies number of zero
- filled pages written to this disk. No memory is allocated for
- such pages.
+ The same_pages file is read-only and specifies number of same
+ element filled pages written to this disk. No memory is allocated
+ for such pages.
What: /sys/block/zram<id>/orig_data_size
Date: August 2010
Contact: Nitin Gupta <ngupta@xxxxxxxxxx>
Description:
The orig_data_size file is read-only and specifies uncompressed
- size of data stored in this disk. This excludes zero-filled
- pages (zero_pages) since no memory is allocated for them.
+ size of data stored in this disk. This excludes same-element-filled
+ pages (same_pages) since no memory is allocated for them.
Unit: bytes
What: /sys/block/zram<id>/compr_data_size
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 0535ae1..e93a7ff 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -170,7 +170,7 @@ max_comp_streams RW the number of possible concurrent compress operations
comp_algorithm RW show and change the compression algorithm
notify_free RO the number of notifications to free pages (either
slot free notifications or REQ_DISCARD requests)
-zero_pages RO the number of zero filled pages written to this disk
+same_pages RO the number of same element filled pages written to this disk
orig_data_size RO uncompressed size of data stored in this disk
compr_data_size RO compressed size of data stored in this disk
mem_used_total RO the amount of memory allocated for this disk
@@ -225,7 +225,7 @@ line of text and contains the following stats separated by whitespace:
mem_used_total
mem_limit
mem_used_max
- zero_pages
+ same_pages
num_migrated
9) Deactivate:
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 15f58ab..a72ecf1 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -94,6 +94,17 @@ 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);
@@ -158,31 +169,76 @@ 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 = PAGE_SIZE / sizeof(unsigned long) - 1; i >= 0; i--)
+ page[i] = value;
+ }
+}
+
+static inline void zram_set_page_partial(char *ptr, unsigned int size,
+ unsigned long value)
+{
+ int i;
+
+ if (likely(value == 0)) {
+ memset(ptr, 0, size);
+ return;
+ }
+
+ i = ((unsigned long)ptr) % sizeof(unsigned long);
+ if (i) {
+ while (i < sizeof(unsigned long)) {
+ *ptr++ = (value >> (i * 8)) & 0xff;
+ --size;
+ ++i;
+ }
+ }
+
+ for (i = size / sizeof(unsigned long); i > 0; --i) {
+ *(unsigned long *)ptr = value;
+ ptr += sizeof(unsigned long);
+ size -= sizeof(unsigned long);
+ }
+
+ 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 = PAGE_SIZE / sizeof(unsigned long) - 1; pos > 0; pos--) {
+ if (page[pos] != page[pos - 1])
return false;
}
+ element[0] = 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_set_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);
@@ -431,7 +487,7 @@ 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);
@@ -464,7 +520,7 @@ 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)
@@ -538,18 +594,20 @@ 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 (!handle)
+ return;
+
zs_free(meta->mem_pool, handle);
atomic64_sub(zram_get_obj_size(meta, index),
@@ -572,9 +630,9 @@ 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;
}
@@ -610,9 +668,9 @@ 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);
@@ -660,6 +718,7 @@ 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)) {
@@ -688,16 +747,17 @@ 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;
}
@@ -1203,7 +1263,7 @@ 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