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* [PATCH zram] extend zero pages to same element pages
From: zhouxianrong @ 2017-01-04  6:20 UTC (permalink / raw)
  Cc: linux-kernel, minchan, ngupta, zhouxianrong, zhouxiyu, weidu.du,
	zhangshiming5, won.ho.park

From: z00281421 <z00281421@notesmail.huawei.com>


Signed-off-by: z00281421 <z00281421@notesmail.huawei.com>
---
 drivers/block/zram/zram_drv.c |   67 ++++++++++++++++++++++++++---------------
 drivers/block/zram/zram_drv.h |   11 ++++---
 2 files changed, 49 insertions(+), 29 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 15f58ab..c3af69a 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 +169,31 @@ static inline void update_used_max(struct zram *zram,
 	} while (old_max != cur_max);
 }
 
-static bool page_zero_filled(void *ptr)
+static bool page_same_filled(void *ptr)
 {
 	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;
 	}
 
 	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);
+		memset(user_mem + bvec->bv_offset, (char)element, bvec->bv_len);
 	else
-		clear_page(user_mem);
+		memset(user_mem, (char)element, PAGE_SIZE);
 	kunmap_atomic(user_mem);
 
 	flush_dcache_page(page);
@@ -431,7 +442,7 @@ 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 +475,7 @@ 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 +549,20 @@ 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 +585,9 @@ 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);
+		memset(mem, (char)meta->table[index].element, PAGE_SIZE);
 		return 0;
 	}
 
@@ -610,9 +623,9 @@ 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);
@@ -688,16 +701,20 @@ 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)) {
+		unsigned long element;
+
+		element = uncmem[0];
 		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 +1220,7 @@ 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

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