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[PATCH 2/5] zram: partial IO refactoring

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  [PATCH 2/5] zram: partial IO refactoring Minchan Kim <minchan@kernel.org> - 2017-04-03 07:20 +0200
    Re: [PATCH 2/5] zram: partial IO refactoring Minchan Kim <minchan@kernel.org> - 2017-04-03 08:20 +0200
    Re: [PATCH 2/5] zram: partial IO refactoring Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-04 04:20 +0200
      Re: [PATCH 2/5] zram: partial IO refactoring Minchan Kim <minchan@kernel.org> - 2017-04-04 07:00 +0200

#1614885 — [PATCH 2/5] zram: partial IO refactoring

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
+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);
-- 
2.7.4

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#1614903

Hi Mika,

On Mon, Apr 03, 2017 at 08:52:33AM +0300, Mika Penttilä wrote:
> 
> 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). ? 

zram declares this.

        #define ZRAM_LOGICAL_BLOCK_SIZE (1<<12)

	blk_queue_physical_block_size(zram->disk->queue, PAGE_SIZE);
	blk_queue_logical_block_size(zram->disk->queue,
					ZRAM_LOGICAL_BLOCK_SIZE);

So, I thought there is no such partial IO in 4096 page architecture.
Am I missing something? Could you tell the scenario if it happens?

Thanks!

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#1615658

Hello,

On (04/03/17 14:17), Minchan Kim wrote:
> +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;
> +}

zram_special_page_read() and zram_special_page_write() have a slightly
different locking semantics.

zram_special_page_read() copy-out ZRAM_SAME page having slot unlocked
(can the slot got overwritten in the meantime?), while
zram_special_page_write() keeps the slot locked through out the entire
operation.

>  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))

so, I think zram_bvec_read() path calls zram_special_page_read() twice:

  a) direct zram_special_page_read() call

  b) zram_decompress_page()->zram_special_page_read()

is it supposed to be so?

>  		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)

ok, I see why... not super happy with the `zstrm' magic, but OK. can do.

	-ss

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#1615705

Hi Sergey,

On Tue, Apr 04, 2017 at 11:17:06AM +0900, Sergey Senozhatsky wrote:
> Hello,
> 
> On (04/03/17 14:17), Minchan Kim wrote:
> > +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;
> > +}
> 
> zram_special_page_read() and zram_special_page_write() have a slightly
> different locking semantics.
> 
> zram_special_page_read() copy-out ZRAM_SAME page having slot unlocked
> (can the slot got overwritten in the meantime?), while

IMHO, yes, it can be overwritten but it doesn't make corruption of kernel.
I mean if such race happens, it's user fault who should protect the race.
zRAM is dumb block device so it can read/write block user request but
one thing we should keep the promise is it shouldn't corrupt the kernel.
Such pov, zram_special_page_read wouldn't be a problem to return
stale data, I think.

> zram_special_page_write() keeps the slot locked through out the entire
> operation.

zram_special_page_write is something different because it updates
zram_table's slot via zram_set_[flag|element] so it should be protected
by zram.

> 
> >  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))
> 
> so, I think zram_bvec_read() path calls zram_special_page_read() twice:
> 
>   a) direct zram_special_page_read() call
> 
>   b) zram_decompress_page()->zram_special_page_read()
> 
> is it supposed to be so?

Yes, Because zram_decompress_page is called by zram_bvec_write
in case of partial IO. Maybe, we makes it simple with removing
zram_special_page_read in zram_bvec_read. I will look.

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