Re: [PATCH] mm: extend zero pages to same element pages for zram
From: zhouxianrong
Date: Mon Feb 06 2017 - 21:25:10 EST
On 2017/2/7 7:48, Minchan Kim wrote:
Hi
On Mon, Feb 06, 2017 at 09:28:18AM +0800, zhouxianrong wrote:
On 2017/2/5 22:21, Minchan Kim wrote:
Hi zhouxianrong,
On Fri, Feb 03, 2017 at 04:42:27PM +0800, zhouxianrong@xxxxxxxxxx wrote:
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
The description in old version was better for justifying same page merging
feature.
Signed-off-by: zhouxianrong <zhouxianrong@xxxxxxxxxx>
---
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
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
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?
}
@@ -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
.
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.