On 2017/2/7 7:48, Minchan Kim wrote:

Hi

On Mon, Feb 06, 2017 at 09:28:18AM +0800, zhouxianrong wrote:

quoted

On 2017/2/5 22:21, Minchan Kim wrote:

quoted

Hi zhouxianrong,

On Fri, Feb 03, 2017 at 04:42:27PM +0800, zhouxianrong@huawei.com wrote:

quoted

From: zhouxianrong <redacted>

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

The description in old version was better for justifying same page merging
feature.

quoted

Signed-off-by: zhouxianrong <redacted>
---
drivers/block/zram/zram_drv.c |  124 +++++++++++++++++++++++++++++++----------
drivers/block/zram/zram_drv.h |   11 ++--
2 files changed, 103 insertions(+), 32 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index e5ab7d9..6a8c9c5 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;
+		}
+	}
+

I don't think we need this part because block layer works with sector
size or multiple times of it so it must be aligned unsigned long.




.

Minchan and Matthew Wilcox:

1. right, but users could open /dev/block/zram0 file and do any read operations.

Could you make that happen?
I don't think it's possible as Matthew already pointed out, too.

yes, Matthew is right, thanks

quoted

2. about endian operation for long, the modification is trivial and low efficient.
   i have not better method. do you have any good idea for this?

So if assumption 1 is wrong, we don't need 2, either.

yes

quoted

3. the below should be modified.

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);

Could you explain why we need this modification?

quoted

 	}

@@ -511,7 +575,7 @@ static void zram_meta_free(struct zram_meta *meta, u64 disksize)
 static struct zram_meta *zram_meta_alloc(char *pool_name, u64 disksize)
 {
 	size_t num_pages;
-	struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
+	struct zram_meta *meta = kzalloc(sizeof(*meta), GFP_KERNEL);

Ditto

quoted

.

because of union of handle and element, i think a non-zero element (other than handle) is prevented from freeing.
if zram_meta_get was modified, zram_meta_alloc did so.

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