Re: [PATCH 4/4] zram: make deduplication feature optional

[Minchan Kim <minchan@kernel.org>]

On Thu, Mar 16, 2017 at 11:46:38AM +0900, js1304@gmail.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> 
> Benefit of deduplication is dependent on the workload so it's not
> preferable to always enable. Therefore, make it optional.

Please make it to Kconfig, too. And write down the description to impress
"help a lot for users who uses zram to build output directory"
And the feature should be disabled as default.

> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> ---
>  drivers/block/zram/zram_drv.c | 80 ++++++++++++++++++++++++++++++++++++++-----
>  drivers/block/zram/zram_drv.h |  1 +
>  2 files changed, 73 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 012425f..e45aa9f 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -328,6 +328,39 @@ static ssize_t comp_algorithm_store(struct device *dev,
>  	return len;
>  }
>  
> +static ssize_t use_dedup_show(struct device *dev,
> +		struct device_attribute *attr, char *buf)
> +{
> +	int val;
> +	struct zram *zram = dev_to_zram(dev);
> +
> +	down_read(&zram->init_lock);
> +	val = zram->use_dedup;
> +	up_read(&zram->init_lock);
> +
> +	return scnprintf(buf, PAGE_SIZE, "%d\n", val);
> +}
> +
> +static ssize_t use_dedup_store(struct device *dev,
> +		struct device_attribute *attr, const char *buf, size_t len)
> +{
> +	int val;
> +	struct zram *zram = dev_to_zram(dev);
> +
> +	if (kstrtoint(buf, 10, &val) || (val != 0 && val != 1))
> +		return -EINVAL;
> +
> +	down_write(&zram->init_lock);
> +	if (init_done(zram)) {
> +		up_write(&zram->init_lock);
> +		pr_info("Can't change dedup usage for initialized device\n");
> +		return -EBUSY;
> +	}
> +	zram->use_dedup = val;
> +	up_write(&zram->init_lock);
> +	return len;
> +}
> +
>  static ssize_t compact_store(struct device *dev,
>  		struct device_attribute *attr, const char *buf, size_t len)
>  {
> @@ -422,11 +455,23 @@ static ssize_t debug_stat_show(struct device *dev,
>  static DEVICE_ATTR_RO(mm_stat);
>  static DEVICE_ATTR_RO(debug_stat);
>  
> -static u32 zram_calc_checksum(unsigned char *mem)
> +static u32 zram_calc_checksum(struct zram *zram, unsigned char *mem)
>  {
> +	if (!zram->use_dedup)
> +		return 0;
> +

Hmm, I don't like this style which every dedup functions have the check
"use_dedup".

Can't we abstract like this?

I want to find more simple way to no need to add the check when new dedup
functions pop up.

bool zram_dedup_check
        if (!zram->dedup)
                return false;

        zram_dedup_checksum
        entry = zram_dedup_get
        if (!entry) {
                zram_dedup_add
                return false;
        }
        ..
        return true;


zram_bvec_write:
        ...
        ...

        if (zram_dedup_match())
                goto found_dup;



>  	return jhash(mem, PAGE_SIZE, 0);
>  }
>  
> +static unsigned long zram_entry_handle(struct zram *zram,
> +				struct zram_entry *entry)
> +{
> +	if (!zram->use_dedup)
> +		return (unsigned long)entry;
> +
> +	return entry->handle;
> +}
> +
>  static struct zram_entry *zram_entry_alloc(struct zram *zram,
>  					unsigned int len, gfp_t flags)
>  {
> @@ -438,6 +483,9 @@ static struct zram_entry *zram_entry_alloc(struct zram *zram,
>  	if (!handle)
>  		return NULL;
>  
> +	if (!zram->use_dedup)
> +		return (struct zram_entry *)handle;
> +
>  	entry = kzalloc(sizeof(*entry), flags);
>  	if (!entry) {
>  		zs_free(meta->mem_pool, handle);
> @@ -462,6 +510,9 @@ static void zram_entry_insert(struct zram *zram, struct zram_entry *new,
>  	struct rb_node **rb_node, *parent = NULL;
>  	struct zram_entry *entry;
>  
> +	if (!zram->use_dedup)
> +		return;
> +
>  	new->checksum = checksum;
>  	hash = &meta->hash[checksum % meta->hash_size];
>  	rb_root = &hash->rb_root;
> @@ -492,7 +543,8 @@ static bool zram_entry_match(struct zram *zram, struct zram_entry *entry,
>  	struct zram_meta *meta = zram->meta;
>  	struct zcomp_strm *zstrm;
>  
> -	cmem = zs_map_object(meta->mem_pool, entry->handle, ZS_MM_RO);
> +	cmem = zs_map_object(meta->mem_pool,
> +			zram_entry_handle(zram, entry), ZS_MM_RO);
>  	if (entry->len == PAGE_SIZE) {
>  		match = !memcmp(mem, cmem, PAGE_SIZE);
>  	} else {
> @@ -501,7 +553,7 @@ static bool zram_entry_match(struct zram *zram, struct zram_entry *entry,
>  			match = !memcmp(mem, zstrm->buffer, PAGE_SIZE);
>  		zcomp_stream_put(zram->comp);
>  	}
> -	zs_unmap_object(meta->mem_pool, entry->handle);
> +	zs_unmap_object(meta->mem_pool, zram_entry_handle(zram, entry));
>  
>  	return match;
>  }
> @@ -521,6 +573,11 @@ static bool zram_entry_put(struct zram *zram, struct zram_meta *meta,
>  	struct zram_hash *hash;
>  	u32 checksum;
>  
> +	if (!zram->use_dedup) {
> +		zs_free(meta->mem_pool, zram_entry_handle(zram, entry));
> +		return false;
> +	}
> +
>  	if (!populated)
>  		goto free;
>  
> @@ -551,6 +608,9 @@ static struct zram_entry *zram_entry_get(struct zram *zram,
>  	struct zram_entry *entry;
>  	struct rb_node *rb_node;
>  
> +	if (!zram->use_dedup)
> +		return NULL;
> +
>  	hash = &meta->hash[checksum % meta->hash_size];
>  
>  	spin_lock(&hash->lock);
> @@ -713,7 +773,8 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
>  		return 0;
>  	}
>  
> -	cmem = zs_map_object(meta->mem_pool, entry->handle, ZS_MM_RO);
> +	cmem = zs_map_object(meta->mem_pool,
> +			zram_entry_handle(zram, entry), ZS_MM_RO);
>  	if (size == PAGE_SIZE) {
>  		copy_page(mem, cmem);
>  	} else {
> @@ -722,7 +783,7 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
>  		ret = zcomp_decompress(zstrm, cmem, size, mem);
>  		zcomp_stream_put(zram->comp);
>  	}
> -	zs_unmap_object(meta->mem_pool, entry->handle);
> +	zs_unmap_object(meta->mem_pool, zram_entry_handle(zram, entry));
>  	bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
>  
>  	/* Should NEVER happen. Return bio error if it does. */
> @@ -840,7 +901,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>  		goto out;
>  	}
>  
> -	checksum = zram_calc_checksum(uncmem);
> +	checksum = zram_calc_checksum(zram, uncmem);
>  	if (!entry) {
>  		entry = zram_entry_get(zram, uncmem, checksum);
>  		if (entry) {
> @@ -915,7 +976,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>  		goto out;
>  	}
>  
> -	cmem = zs_map_object(meta->mem_pool, entry->handle, ZS_MM_WO);
> +	cmem = zs_map_object(meta->mem_pool,
> +			zram_entry_handle(zram, entry), ZS_MM_WO);
>  
>  	if ((clen == PAGE_SIZE) && !is_partial_io(bvec)) {
>  		src = kmap_atomic(page);
> @@ -927,7 +989,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>  
>  	zcomp_stream_put(zram->comp);
>  	zstrm = NULL;
> -	zs_unmap_object(meta->mem_pool, entry->handle);
> +	zs_unmap_object(meta->mem_pool, zram_entry_handle(zram, entry));
>  	zram_entry_insert(zram, entry, checksum);
>  
>  found_duplication:
> @@ -1310,6 +1372,7 @@ static int zram_open(struct block_device *bdev, fmode_t mode)
>  static DEVICE_ATTR_WO(mem_used_max);
>  static DEVICE_ATTR_RW(max_comp_streams);
>  static DEVICE_ATTR_RW(comp_algorithm);
> +static DEVICE_ATTR_RW(use_dedup);
>  
>  static struct attribute *zram_disk_attrs[] = {
>  	&dev_attr_disksize.attr,
> @@ -1320,6 +1383,7 @@ static int zram_open(struct block_device *bdev, fmode_t mode)
>  	&dev_attr_mem_used_max.attr,
>  	&dev_attr_max_comp_streams.attr,
>  	&dev_attr_comp_algorithm.attr,
> +	&dev_attr_use_dedup.attr,
>  	&dev_attr_io_stat.attr,
>  	&dev_attr_mm_stat.attr,
>  	&dev_attr_debug_stat.attr,
> diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
> index 07d1f8d..b823555 100644
> --- a/drivers/block/zram/zram_drv.h
> +++ b/drivers/block/zram/zram_drv.h
> @@ -141,5 +141,6 @@ struct zram {
>  	 * zram is claimed so open request will be failed
>  	 */
>  	bool claim; /* Protected by bdev->bd_mutex */
> +	int use_dedup;

For binary result, I want to use 'bool'

>  };
>  #endif
> -- 
> 1.9.1
>