Re: [PATCH -next] zram: do not pass rw argument to__zram_make_request()

From: Sergey Senozhatsky
Date: Fri Jan 10 2014 - 04:03:55 EST

On (01/10/14 16:14), Minchan Kim wrote:
> On Thu, Jan 09, 2014 at 04:23:43PM +0300, Sergey Senozhatsky wrote:
> > Do not pass rw argument down the __zram_make_request() -> zram_bvec_rw()
> > chain, decode it in zram_bvec_rw() instead. Besides, this is the place
> > where we distinguish READ and WRITE bio data directions, so account zram
> > RW stats here, instead of __zram_make_request(). This also allows to
> > account a real number of zram READ/WRITE operations, not just requests
> > (RW request may end up in a number of zram RW ops with separate
> > locking, compression/decompression, slot free handling, etc).
>
> Looks sane to me because other statistic variable accounts per bio, not
> request. But it changes current statistic's semantic so they could be
> regressed. Let's wait a bit for other's opinion.
>

Hello,

well, imho current zram stats are a bit meaningless and misleading. some data
simply makes a little sense, some data is not visible to end user at all, etc. my
plan was to revisit it before 3.14 merge window (which is also the end of promotion,
I guess). after 3.14 merge window we will not be able to change this easily.

I was going to publish stats rework patch today. It removes code duplication
and re-organizes end user visible stats. so here it is (w/o the proper commit
message)

num_reads
num_writes
pages_stored
invalid_io
notify_free
pages_zero
compressed_size
memory_used

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>

---

drivers/block/zram/zram_drv.c | 171 +++++++++++-------------------------------
drivers/block/zram/zram_drv.h | 15 ++--
2 files changed, 51 insertions(+), 135 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 798793f..234e703 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -42,6 +42,17 @@ static struct zram *zram_devices;
/* Module params (documentation at end) */
static unsigned int num_devices = 1;

+#define ZRAM_ATTR_RO(name) \
+static ssize_t zram_attr_##name##_show(struct device *d, \
+ struct device_attribute *attr, char *b) \
+{ \
+ struct zram *zram = dev_to_zram(d); \
+ return sprintf(b, "%llu\n", \
+ (u64)atomic64_read(&zram->stats.name)); \
+} \
+static struct device_attribute dev_attr_##name = \
+ __ATTR(name, S_IRUGO, zram_attr_##name##_show, NULL);
+
static inline int init_done(struct zram *zram)
{
return zram->meta != NULL;
@@ -52,97 +63,31 @@ static inline struct zram *dev_to_zram(struct device *dev)
return (struct zram *)dev_to_disk(dev)->private_data;
}

-static ssize_t disksize_show(struct device *dev,
- struct device_attribute *attr, char *buf)
-{
- struct zram *zram = dev_to_zram(dev);
-
- return sprintf(buf, "%llu\n", zram->disksize);
-}
-
-static ssize_t initstate_show(struct device *dev,
- struct device_attribute *attr, char *buf)
-{
- struct zram *zram = dev_to_zram(dev);
-
- return sprintf(buf, "%u\n", init_done(zram));
-}
-
-static ssize_t num_reads_show(struct device *dev,
- struct device_attribute *attr, char *buf)
-{
- struct zram *zram = dev_to_zram(dev);
-
- return sprintf(buf, "%llu\n",
- (u64)atomic64_read(&zram->stats.num_reads));
-}
-
-static ssize_t num_writes_show(struct device *dev,
- struct device_attribute *attr, char *buf)
-{
- struct zram *zram = dev_to_zram(dev);
-
- return sprintf(buf, "%llu\n",
- (u64)atomic64_read(&zram->stats.num_writes));
-}
-
-static ssize_t invalid_io_show(struct device *dev,
- struct device_attribute *attr, char *buf)
-{
- struct zram *zram = dev_to_zram(dev);
-
- return sprintf(buf, "%llu\n",
- (u64)atomic64_read(&zram->stats.invalid_io));
-}
-
-static ssize_t notify_free_show(struct device *dev,
- struct device_attribute *attr, char *buf)
-{
- struct zram *zram = dev_to_zram(dev);
-
- return sprintf(buf, "%llu\n",
- (u64)atomic64_read(&zram->stats.notify_free));
-}
-
-static ssize_t zero_pages_show(struct device *dev,
- struct device_attribute *attr, char *buf)
-{
- struct zram *zram = dev_to_zram(dev);
-
- return sprintf(buf, "%u\n", zram->stats.pages_zero);
-}
-
-static ssize_t orig_data_size_show(struct device *dev,
- struct device_attribute *attr, char *buf)
+static ssize_t memory_used_show(struct device *dev, struct device_attribute *attr, char *buf)
{
+ u64 val = 0;
struct zram *zram = dev_to_zram(dev);
+ struct zram_meta *meta = zram->meta;

- return sprintf(buf, "%llu\n",
- (u64)(zram->stats.pages_stored) << PAGE_SHIFT);
+ down_read(&zram->init_lock);
+ if (init_done(zram))
+ val = zs_get_total_size_bytes(meta->mem_pool);
+ up_read(&zram->init_lock);
+ return sprintf(buf, "%llu\n", val);
}

-static ssize_t compr_data_size_show(struct device *dev,
+static ssize_t disksize_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct zram *zram = dev_to_zram(dev);
-
- return sprintf(buf, "%llu\n",
- (u64)atomic64_read(&zram->stats.compr_size));
+ return sprintf(buf, "%llu\n", zram->disksize);
}

-static ssize_t mem_used_total_show(struct device *dev,
+static ssize_t initstate_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
- u64 val = 0;
struct zram *zram = dev_to_zram(dev);
- struct zram_meta *meta = zram->meta;
-
- down_read(&zram->init_lock);
- if (init_done(zram))
- val = zs_get_total_size_bytes(meta->mem_pool);
- up_read(&zram->init_lock);
-
- return sprintf(buf, "%llu\n", val);
+ return sprintf(buf, "%u\n", init_done(zram));
}

static int zram_test_flag(struct zram_meta *meta, u32 index,
@@ -289,7 +234,6 @@ static void zram_free_page(struct zram *zram, size_t index)
{
struct zram_meta *meta = zram->meta;
unsigned long handle = meta->table[index].handle;
- u16 size = meta->table[index].size;

if (unlikely(!handle)) {
/*
@@ -298,21 +242,14 @@ static void zram_free_page(struct zram *zram, size_t index)
*/
if (zram_test_flag(meta, index, ZRAM_ZERO)) {
zram_clear_flag(meta, index, ZRAM_ZERO);
- zram->stats.pages_zero--;
+ atomic64_dec(&zram->stats.pages_zero);
}
return;
}

- if (unlikely(size > max_zpage_size))
- zram->stats.bad_compress--;
-
zs_free(meta->mem_pool, handle);
-
- if (size <= PAGE_SIZE / 2)
- zram->stats.good_compress--;
-
- atomic64_sub(meta->table[index].size, &zram->stats.compr_size);
- zram->stats.pages_stored--;
+ atomic64_sub(meta->table[index].size, &zram->stats.compressed_size);
+ atomic64_dec(&zram->stats.pages_stored);

meta->table[index].handle = 0;
meta->table[index].size = 0;
@@ -352,7 +289,7 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
u32 index, int offset, struct bio *bio)
{
- int ret;
+ int ret = -EINVAL;
struct page *page;
unsigned char *user_mem, *uncmem = NULL;
struct zram_meta *meta = zram->meta;
@@ -393,6 +330,8 @@ out_cleanup:
kunmap_atomic(user_mem);
if (is_partial_io(bvec))
kfree(uncmem);
+ if (ret)
+ atomic64_inc(&zram->stats.failed_reads);
return ret;
}

@@ -440,7 +379,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
/* Free memory associated with this sector now. */
zram_free_page(zram, index);

- zram->stats.pages_zero++;
+ atomic64_inc(&zram->stats.pages_zero);
zram_set_flag(meta, index, ZRAM_ZERO);
ret = 0;
goto out;
@@ -469,7 +408,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
}

if (unlikely(clen > max_zpage_size)) {
- zram->stats.bad_compress++;
clen = PAGE_SIZE;
src = NULL;
if (is_partial_io(bvec))
@@ -503,17 +441,12 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,

meta->table[index].handle = handle;
meta->table[index].size = clen;
-
/* Update stats */
- atomic64_add(clen, &zram->stats.compr_size);
- zram->stats.pages_stored++;
- if (clen <= PAGE_SIZE / 2)
- zram->stats.good_compress++;
-
+ atomic64_add(clen, &zram->stats.compressed_size);
+ atomic64_inc(&zram->stats.pages_stored);
out:
if (is_partial_io(bvec))
kfree(uncmem);
-
if (ret)
atomic64_inc(&zram->stats.failed_writes);
return ret;
@@ -594,23 +527,8 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)

static void zram_init_device(struct zram *zram, struct zram_meta *meta)
{
- if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
- pr_info(
- "There is little point creating a zram of greater than "
- "twice the size of memory since we expect a 2:1 compression "
- "ratio. Note that zram uses about 0.1%% of the size of "
- "the disk when not in use so a huge zram is "
- "wasteful.\n"
- "\tMemory Size: %lu kB\n"
- "\tSize you selected: %llu kB\n"
- "Continuing anyway ...\n",
- (totalram_pages << PAGE_SHIFT) >> 10, zram->disksize >> 10
- );
- }
-
/* zram devices sort of resembles non-rotational disks */
queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
-
zram->meta = meta;
pr_debug("Initialization done!\n");
}
@@ -803,14 +721,15 @@ static DEVICE_ATTR(disksize, S_IRUGO | S_IWUSR,
disksize_show, disksize_store);
static DEVICE_ATTR(initstate, S_IRUGO, initstate_show, NULL);
static DEVICE_ATTR(reset, S_IWUSR, NULL, reset_store);
-static DEVICE_ATTR(num_reads, S_IRUGO, num_reads_show, NULL);
-static DEVICE_ATTR(num_writes, S_IRUGO, num_writes_show, NULL);
-static DEVICE_ATTR(invalid_io, S_IRUGO, invalid_io_show, NULL);
-static DEVICE_ATTR(notify_free, S_IRUGO, notify_free_show, NULL);
-static DEVICE_ATTR(zero_pages, S_IRUGO, zero_pages_show, NULL);
-static DEVICE_ATTR(orig_data_size, S_IRUGO, orig_data_size_show, NULL);
-static DEVICE_ATTR(compr_data_size, S_IRUGO, compr_data_size_show, NULL);
-static DEVICE_ATTR(mem_used_total, S_IRUGO, mem_used_total_show, NULL);
+static DEVICE_ATTR(memory_used, S_IRUGO, memory_used_show, NULL);
+
+ZRAM_ATTR_RO(num_reads);
+ZRAM_ATTR_RO(num_writes);
+ZRAM_ATTR_RO(pages_stored);
+ZRAM_ATTR_RO(invalid_io);
+ZRAM_ATTR_RO(notify_free);
+ZRAM_ATTR_RO(pages_zero);
+ZRAM_ATTR_RO(compressed_size);

static struct attribute *zram_disk_attrs[] = {
&dev_attr_disksize.attr,
@@ -818,12 +737,12 @@ static struct attribute *zram_disk_attrs[] = {
&dev_attr_reset.attr,
&dev_attr_num_reads.attr,
&dev_attr_num_writes.attr,
+ &dev_attr_pages_stored.attr,
&dev_attr_invalid_io.attr,
&dev_attr_notify_free.attr,
- &dev_attr_zero_pages.attr,
- &dev_attr_orig_data_size.attr,
- &dev_attr_compr_data_size.attr,
- &dev_attr_mem_used_total.attr,
+ &dev_attr_pages_zero.attr,
+ &dev_attr_compressed_size.attr,
+ &dev_attr_memory_used.attr,
NULL,
};

diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 1388bad..6b00d4d 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -64,8 +64,7 @@ enum zram_pageflags {
struct table {
unsigned long handle;
u16 size; /* object size (excluding header) */
- u8 count; /* object ref count (not yet used) */
- u8 flags;
+ u16 flags;
} __aligned(4);

/*
@@ -73,17 +72,15 @@ struct table {
* All modifications to 32bit counter should be protected by zram->lock.
*/
struct zram_stats {
- atomic64_t compr_size; /* compressed size of pages stored */
- atomic64_t num_reads; /* failed + successful */
- atomic64_t num_writes; /* --do-- */
+ atomic64_t num_writes; /* number of writes */
+ atomic64_t num_reads; /* number of reads */
+ atomic64_t pages_stored; /* no. of pages currently stored */
+ atomic64_t compressed_size; /* compressed size of pages stored */
+ atomic64_t pages_zero; /* no. of zero filled pages */
atomic64_t failed_reads; /* should NEVER! happen */
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 */
- u32 pages_zero; /* no. of zero filled pages */
- u32 pages_stored; /* no. of pages currently stored */
- u32 good_compress; /* % of pages with compression ratio<=50% */
- u32 bad_compress; /* % of pages with compression ratio>=75% */
};

struct zram_meta {

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