Subject: Re: [PATCH 2/5] zram: partial IO refactoring
To: Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
References: <1491196653-7388-1-git-send-email-minchan@kernel.org>
 <1491196653-7388-3-git-send-email-minchan@kernel.org>
CC: <linux-kernel@vger.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        <kernel-team@lge.com>
From: =?UTF-8?Q?Mika_Penttil=c3=a4?= <mika.penttila@nextfour.com>
Message-ID: <db97345f-f97d-fb1e-c2c4-a05af28333de@nextfour.com>
Date: Mon, 3 Apr 2017 08:52:33 +0300
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Hi!

On 04/03/2017 08:17 AM, Minchan Kim wrote:
> For architecture(PAGE_SIZE > 4K), zram have supported partial IO.
> However, the mixed code for handling normal/partial IO is too mess,
> error-prone to modify IO handler functions with upcoming feature
> so this patch aims for cleaning up zram's IO handling functions.
> 
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  drivers/block/zram/zram_drv.c | 333 +++++++++++++++++++++++-------------------
>  1 file changed, 184 insertions(+), 149 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 28c2836f8c96..7938f4b98b01 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -45,6 +45,8 @@ static const char *default_compressor = "lzo";
>  /* Module params (documentation at end) */
>  static unsigned int num_devices = 1;
>  
> +static void zram_free_page(struct zram *zram, size_t index);
> +
>  static inline bool init_done(struct zram *zram)
>  {
>  	return zram->disksize;
> @@ -98,10 +100,17 @@ static void zram_set_obj_size(struct zram_meta *meta,
>  	meta->table[index].value = (flags << ZRAM_FLAG_SHIFT) | size;
>  }
>  
> +#if PAGE_SIZE != 4096
>  static inline bool is_partial_io(struct bio_vec *bvec)
>  {
>  	return bvec->bv_len != PAGE_SIZE;
>  }
> +#else

For page size of 4096 bv_len can still be < 4096 and partial pages should be supported 
(uncompress before write etc). ? 

> +static inline bool is_partial_io(struct bio_vec *bvec)
> +{
> +	return false;
> +}
> +#endif
>  
>  static void zram_revalidate_disk(struct zram *zram)
>  {
> @@ -191,18 +200,6 @@ static bool page_same_filled(void *ptr, unsigned long *element)
>  	return true;
>  }
>  
> -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);
> -	zram_fill_page(user_mem + bvec->bv_offset, bvec->bv_len, element);
> -	kunmap_atomic(user_mem);
> -
> -	flush_dcache_page(page);
> -}
> -
>  static ssize_t initstate_show(struct device *dev,
>  		struct device_attribute *attr, char *buf)
>  {
> @@ -418,6 +415,53 @@ static DEVICE_ATTR_RO(io_stat);
>  static DEVICE_ATTR_RO(mm_stat);
>  static DEVICE_ATTR_RO(debug_stat);
>  
> +static bool zram_special_page_read(struct zram *zram, u32 index,
> +				struct page *page,
> +				unsigned int offset, unsigned int len)
> +{
> +	struct zram_meta *meta = zram->meta;
> +
> +	bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
> +	if (unlikely(!meta->table[index].handle) ||
> +			zram_test_flag(meta, index, ZRAM_SAME)) {
> +		void *mem;
> +
> +		bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
> +		mem = kmap_atomic(page);
> +		zram_fill_page(mem + offset, len, meta->table[index].element);
> +		kunmap_atomic(mem);
> +		return true;
> +	}
> +	bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
> +
> +	return false;
> +}
> +
> +static bool zram_special_page_write(struct zram *zram, u32 index,
> +					struct page *page)
> +{
> +	unsigned long element;
> +	void *mem = kmap_atomic(page);
> +
> +	if (page_same_filled(mem, &element)) {
> +		struct zram_meta *meta = zram->meta;
> +
> +		kunmap_atomic(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_SAME);
> +		zram_set_element(meta, index, element);
> +		bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
> +
> +		atomic64_inc(&zram->stats.same_pages);
> +		return true;
> +	}
> +	kunmap_atomic(mem);
> +
> +	return false;
> +}
> +
>  static void zram_meta_free(struct zram_meta *meta, u64 disksize)
>  {
>  	size_t num_pages = disksize >> PAGE_SHIFT;
> @@ -504,169 +548,104 @@ static void zram_free_page(struct zram *zram, size_t index)
>  	zram_set_obj_size(meta, index, 0);
>  }
>  
> -static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
> +static int zram_decompress_page(struct zram *zram, struct page *page, u32 index)
>  {
> -	int ret = 0;
> -	unsigned char *cmem;
> -	struct zram_meta *meta = zram->meta;
> +	int ret;
>  	unsigned long handle;
>  	unsigned int size;
> +	void *src, *dst;
> +	struct zram_meta *meta = zram->meta;
> +
> +	if (zram_special_page_read(zram, index, page, 0, PAGE_SIZE))
> +		return 0;
>  
>  	bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
>  	handle = meta->table[index].handle;
>  	size = zram_get_obj_size(meta, index);
>  
> -	if (!handle || zram_test_flag(meta, index, ZRAM_SAME)) {
> -		bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
> -		zram_fill_page(mem, PAGE_SIZE, meta->table[index].element);
> -		return 0;
> -	}
> -
> -	cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_RO);
> +	src = zs_map_object(meta->mem_pool, handle, ZS_MM_RO);
>  	if (size == PAGE_SIZE) {
> -		copy_page(mem, cmem);
> +		dst = kmap_atomic(page);
> +		copy_page(dst, src);
> +		kunmap_atomic(dst);
> +		ret = 0;
>  	} else {
>  		struct zcomp_strm *zstrm = zcomp_stream_get(zram->comp);
>  
> -		ret = zcomp_decompress(zstrm, cmem, size, mem);
> +		dst = kmap_atomic(page);
> +		ret = zcomp_decompress(zstrm, src, size, dst);
> +		kunmap_atomic(dst);
>  		zcomp_stream_put(zram->comp);
>  	}
>  	zs_unmap_object(meta->mem_pool, handle);
>  	bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
>  
>  	/* Should NEVER happen. Return bio error if it does. */
> -	if (unlikely(ret)) {
> +	if (unlikely(ret))
>  		pr_err("Decompression failed! err=%d, page=%u\n", ret, index);
> -		return ret;
> -	}
>  
> -	return 0;
> +	return ret;
>  }
>  
>  static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
> -			  u32 index, int offset)
> +				u32 index, int offset)
>  {
>  	int ret;
>  	struct page *page;
> -	unsigned char *user_mem, *uncmem = NULL;
> -	struct zram_meta *meta = zram->meta;
> -	page = bvec->bv_page;
>  
> -	bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
> -	if (unlikely(!meta->table[index].handle) ||
> -			zram_test_flag(meta, index, ZRAM_SAME)) {
> -		bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
> -		handle_same_page(bvec, meta->table[index].element);
> +	page = bvec->bv_page;
> +	if (zram_special_page_read(zram, index, page, bvec->bv_offset,
> +				bvec->bv_len))
>  		return 0;
> -	}
> -	bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
> -
> -	if (is_partial_io(bvec))
> -		/* Use  a temporary buffer to decompress the page */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
> -
> -	user_mem = kmap_atomic(page);
> -	if (!is_partial_io(bvec))
> -		uncmem = user_mem;
>  
> -	if (!uncmem) {
> -		pr_err("Unable to allocate temp memory\n");
> -		ret = -ENOMEM;
> -		goto out_cleanup;
> +	if (is_partial_io(bvec)) {
> +		/* Use a temporary buffer to decompress the page */
> +		page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
> +		if (!page)
> +			return -ENOMEM;
>  	}
>  
> -	ret = zram_decompress_page(zram, uncmem, index);
> -	/* Should NEVER happen. Return bio error if it does. */
> +	ret = zram_decompress_page(zram, page, index);
>  	if (unlikely(ret))
> -		goto out_cleanup;
> +		goto out;
>  
> -	if (is_partial_io(bvec))
> -		memcpy(user_mem + bvec->bv_offset, uncmem + offset,
> -				bvec->bv_len);
> +	if (is_partial_io(bvec)) {
> +		void *dst = kmap_atomic(bvec->bv_page);
> +		void *src = kmap_atomic(page);
>  
> -	flush_dcache_page(page);
> -	ret = 0;
> -out_cleanup:
> -	kunmap_atomic(user_mem);
> +		memcpy(dst + bvec->bv_offset, src + offset, bvec->bv_len);
> +		kunmap_atomic(src);
> +		kunmap_atomic(dst);
> +	}
> +out:
>  	if (is_partial_io(bvec))
> -		kfree(uncmem);
> +		__free_page(page);
> +
>  	return ret;
>  }
>  
> -static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> -			   int offset)
> +static int zram_compress(struct zram *zram, struct zcomp_strm **zstrm,
> +			struct page *page,
> +			unsigned long *out_handle, unsigned int *out_comp_len)
>  {
> -	int ret = 0;
> -	unsigned int clen;
> +	int ret;
> +	unsigned int comp_len;
> +	void *src;
>  	unsigned long handle = 0;
> -	struct page *page;
> -	unsigned char *user_mem, *cmem, *src, *uncmem = NULL;
>  	struct zram_meta *meta = zram->meta;
> -	struct zcomp_strm *zstrm = NULL;
> -	unsigned long alloced_pages;
> -	unsigned long element;
> -
> -	page = bvec->bv_page;
> -	if (is_partial_io(bvec)) {
> -		/*
> -		 * This is a partial IO. We need to read the full page
> -		 * before to write the changes.
> -		 */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
> -		if (!uncmem) {
> -			ret = -ENOMEM;
> -			goto out;
> -		}
> -		ret = zram_decompress_page(zram, uncmem, index);
> -		if (ret)
> -			goto out;
> -	}
>  
>  compress_again:
> -	user_mem = kmap_atomic(page);
> -	if (is_partial_io(bvec)) {
> -		memcpy(uncmem + offset, user_mem + bvec->bv_offset,
> -		       bvec->bv_len);
> -		kunmap_atomic(user_mem);
> -		user_mem = NULL;
> -	} else {
> -		uncmem = user_mem;
> -	}
> -
> -	if (page_same_filled(uncmem, &element)) {
> -		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_SAME);
> -		zram_set_element(meta, index, element);
> -		bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
> -
> -		atomic64_inc(&zram->stats.same_pages);
> -		ret = 0;
> -		goto out;
> -	}
> -
> -	zstrm = zcomp_stream_get(zram->comp);
> -	ret = zcomp_compress(zstrm, uncmem, &clen);
> -	if (!is_partial_io(bvec)) {
> -		kunmap_atomic(user_mem);
> -		user_mem = NULL;
> -		uncmem = NULL;
> -	}
> +	src = kmap_atomic(page);
> +	ret = zcomp_compress(*zstrm, src, &comp_len);
> +	kunmap_atomic(src);
>  
>  	if (unlikely(ret)) {
>  		pr_err("Compression failed! err=%d\n", ret);
> -		goto out;
> +		return ret;
>  	}
>  
> -	src = zstrm->buffer;
> -	if (unlikely(clen > max_zpage_size)) {
> -		clen = PAGE_SIZE;
> -		if (is_partial_io(bvec))
> -			src = uncmem;
> -	}
> +	if (unlikely(comp_len > max_zpage_size))
> +		comp_len = PAGE_SIZE;
>  
>  	/*
>  	 * handle allocation has 2 paths:
> @@ -682,50 +661,70 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>  	 * from the slow path and handle has already been allocated.
>  	 */
>  	if (!handle)
> -		handle = zs_malloc(meta->mem_pool, clen,
> +		handle = zs_malloc(meta->mem_pool, comp_len,
>  				__GFP_KSWAPD_RECLAIM |
>  				__GFP_NOWARN |
>  				__GFP_HIGHMEM |
>  				__GFP_MOVABLE);
>  	if (!handle) {
>  		zcomp_stream_put(zram->comp);
> -		zstrm = NULL;
> -
>  		atomic64_inc(&zram->stats.writestall);
> -
> -		handle = zs_malloc(meta->mem_pool, clen,
> +		handle = zs_malloc(meta->mem_pool, comp_len,
>  				GFP_NOIO | __GFP_HIGHMEM |
>  				__GFP_MOVABLE);
> +		*zstrm = zcomp_stream_get(zram->comp);
>  		if (handle)
>  			goto compress_again;
> +		return -ENOMEM;
> +	}
>  
> -		pr_err("Error allocating memory for compressed page: %u, size=%u\n",
> -			index, clen);
> -		ret = -ENOMEM;
> -		goto out;
> +	*out_handle = handle;
> +	*out_comp_len = comp_len;
> +	return 0;
> +}
> +
> +static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
> +				u32 index, int offset)
> +{
> +	int ret;
> +	unsigned long handle;
> +	unsigned int comp_len;
> +	void *src, *dst;
> +	struct zcomp_strm *zstrm;
> +	unsigned long alloced_pages;
> +	struct zram_meta *meta = zram->meta;
> +	struct page *page = bvec->bv_page;
> +
> +	if (zram_special_page_write(zram, index, page))
> +		return 0;
> +
> +	zstrm = zcomp_stream_get(zram->comp);
> +	ret = zram_compress(zram, &zstrm, page, &handle, &comp_len);
> +	if (ret) {
> +		zcomp_stream_put(zram->comp);
> +		return ret;
>  	}
>  
>  	alloced_pages = zs_get_total_pages(meta->mem_pool);
>  	update_used_max(zram, alloced_pages);
>  
>  	if (zram->limit_pages && alloced_pages > zram->limit_pages) {
> +		zcomp_stream_put(zram->comp);
>  		zs_free(meta->mem_pool, handle);
> -		ret = -ENOMEM;
> -		goto out;
> +		return -ENOMEM;
>  	}
>  
> -	cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_WO);
> +	dst = zs_map_object(meta->mem_pool, handle, ZS_MM_WO);
>  
> -	if ((clen == PAGE_SIZE) && !is_partial_io(bvec)) {
> +	if (comp_len == PAGE_SIZE) {
>  		src = kmap_atomic(page);
> -		copy_page(cmem, src);
> +		copy_page(dst, src);
>  		kunmap_atomic(src);
>  	} else {
> -		memcpy(cmem, src, clen);
> +		memcpy(dst, zstrm->buffer, comp_len);
>  	}
>  
>  	zcomp_stream_put(zram->comp);
> -	zstrm = NULL;
>  	zs_unmap_object(meta->mem_pool, handle);
>  
>  	/*
> @@ -734,19 +733,54 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>  	 */
>  	bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
>  	zram_free_page(zram, index);
> -
>  	meta->table[index].handle = handle;
> -	zram_set_obj_size(meta, index, clen);
> +	zram_set_obj_size(meta, index, comp_len);
>  	bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
>  
>  	/* Update stats */
> -	atomic64_add(clen, &zram->stats.compr_data_size);
> +	atomic64_add(comp_len, &zram->stats.compr_data_size);
>  	atomic64_inc(&zram->stats.pages_stored);
> +	return 0;
> +}
> +
> +static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
> +				u32 index, int offset)
> +{
> +	int ret;
> +	struct page *page = NULL;
> +	void *src;
> +	struct bio_vec vec;
> +
> +	vec = *bvec;
> +	if (is_partial_io(bvec)) {
> +		void *dst;
> +		/*
> +		 * This is a partial IO. We need to read the full page
> +		 * before to write the changes.
> +		 */
> +		page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
> +		if (!page)
> +			return -ENOMEM;
> +
> +		ret = zram_decompress_page(zram, page, index);
> +		if (ret)
> +			goto out;
> +
> +		src = kmap_atomic(bvec->bv_page);
> +		dst = kmap_atomic(page);
> +		memcpy(dst + offset, src + bvec->bv_offset, bvec->bv_len);
> +		kunmap_atomic(dst);
> +		kunmap_atomic(src);
> +
> +		vec.bv_page = page;
> +		vec.bv_len = PAGE_SIZE;
> +		vec.bv_offset = 0;
> +	}
> +
> +	ret = __zram_bvec_write(zram, &vec, index, offset);
>  out:
> -	if (zstrm)
> -		zcomp_stream_put(zram->comp);
>  	if (is_partial_io(bvec))
> -		kfree(uncmem);
> +		__free_page(page);
>  	return ret;
>  }
>  
> @@ -802,6 +836,7 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
>  	if (!is_write) {
>  		atomic64_inc(&zram->stats.num_reads);
>  		ret = zram_bvec_read(zram, bvec, index, offset);
> +		flush_dcache_page(bvec->bv_page);
>  	} else {
>  		atomic64_inc(&zram->stats.num_writes);
>  		ret = zram_bvec_write(zram, bvec, index, offset);
>