[PATCHv3 0/8] zram: Support multiple compression streams

[PATCHv3 0/8] zram: Support multiple compression streams

[Sergey Senozhatsky]

Hello,

        This series adds support for multiple (per-CPU)
compression streams (at point only 2). The main idea is that
different compression algorithms have different characteristics
and zram may benefit when it uses a combination of algorithms:
a default algorithm that is faster but have lower compression
rate and a secondary algorithm that can use higher compression
rate at a price of slower compression/decompression.

        There are several use-case for this functionality:

- huge pages re-compression: zstd or deflate can successfully
compress huge pages (~50% of huge pages on my synthetic ChromeOS
tests), IOW pages that lzo was not able to compress.

- idle pages re-compression: idle/cold pages sit in the memory
and we may reduce zsmalloc memory usage if we recompress those
idle pages.

        User-space has a number of ways to control the behavior
and impact of zram recompression: what type of pages should be
recompressed, size watermarks, etc. Please refer to documentation
patch.

v3:
-- conditionally reschedule during recompression loop so that
   we don't stall RCU grace periods
-- fixed a false-positive WARN_ON

v2:
-- rebased
-- mark completely incompressible pages (neither default nor secondary
   algorithm can compress them) with a new flag so that we don't attempt
   to recompress them all the time

Sergey Senozhatsky (8):
  zram: Preparation for multi-zcomp support
  zram: Add recompression algorithm sysfs knob
  zram: Factor out WB and non-WB zram read functions
  zram: Introduce recompress sysfs knob
  documentation: Add recompression documentation
  zram: Add recompression algorithm choice to Kconfig
  zram: Add recompress flag to read_block_state()
  zram: correct typos

 Documentation/admin-guide/blockdev/zram.rst |  64 ++-
 drivers/block/zram/Kconfig                  |  52 +++
 drivers/block/zram/zcomp.c                  |   6 +-
 drivers/block/zram/zcomp.h                  |   2 +-
 drivers/block/zram/zram_drv.c               | 441 +++++++++++++++++---
 drivers/block/zram/zram_drv.h               |  16 +-
 6 files changed, 510 insertions(+), 71 deletions(-)

-- 
2.38.0.rc1.362.ged0d419d3c-goog

[PATCHv3 1/8] zram: Preparation for multi-zcomp support

[Sergey Senozhatsky]

The patch turns compression streams and compressor algorithm
name struct zram members into arrays, so that we can have
multiple compression streams support (in the next patches).

The patch uses a rather explicit API for compressor selection:

- Get primary (default) compression stream
	zcomp_stream_get(zram->comps[ZRAM_PRIMARY_ZCOMP])
- Get secondary compression stream
	zcomp_stream_get(zram->comps[ZRAM_SECONDARY_ZCOMP])

We use similar API for compression streams put().

At this point we always have just one compression stream,
since CONFIG_ZRAM_MULTI_COMP is not yet defined.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zcomp.c    |  6 +--
 drivers/block/zram/zcomp.h    |  2 +-
 drivers/block/zram/zram_drv.c | 87 ++++++++++++++++++++++++-----------
 drivers/block/zram/zram_drv.h | 14 +++++-
 4 files changed, 77 insertions(+), 32 deletions(-)

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index 0916de952e09..55af4efd7983 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -206,7 +206,7 @@ void zcomp_destroy(struct zcomp *comp)
  * case of allocation error, or any other error potentially
  * returned by zcomp_init().
  */
-struct zcomp *zcomp_create(const char *compress)
+struct zcomp *zcomp_create(const char *alg)
 {
 	struct zcomp *comp;
 	int error;
@@ -216,14 +216,14 @@ struct zcomp *zcomp_create(const char *compress)
 	 * is not loaded yet. We must do it here, otherwise we are about to
 	 * call /sbin/modprobe under CPU hot-plug lock.
 	 */
-	if (!zcomp_available_algorithm(compress))
+	if (!zcomp_available_algorithm(alg))
 		return ERR_PTR(-EINVAL);
 
 	comp = kzalloc(sizeof(struct zcomp), GFP_KERNEL);
 	if (!comp)
 		return ERR_PTR(-ENOMEM);
 
-	comp->name = compress;
+	comp->name = alg;
 	error = zcomp_init(comp);
 	if (error) {
 		kfree(comp);
diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
index 40f6420f4b2e..cdefdef93da8 100644
--- a/drivers/block/zram/zcomp.h
+++ b/drivers/block/zram/zcomp.h
@@ -27,7 +27,7 @@ int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node);
 ssize_t zcomp_available_show(const char *comp, char *buf);
 bool zcomp_available_algorithm(const char *comp);
 
-struct zcomp *zcomp_create(const char *comp);
+struct zcomp *zcomp_create(const char *alg);
 void zcomp_destroy(struct zcomp *comp);
 
 struct zcomp_strm *zcomp_stream_get(struct zcomp *comp);
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 966aab902d19..770ea3489eb6 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1007,36 +1007,53 @@ static ssize_t comp_algorithm_show(struct device *dev,
 	struct zram *zram = dev_to_zram(dev);
 
 	down_read(&zram->init_lock);
-	sz = zcomp_available_show(zram->compressor, buf);
+	sz = zcomp_available_show(zram->comp_algs[ZRAM_PRIMARY_ZCOMP], buf);
 	up_read(&zram->init_lock);
 
 	return sz;
 }
 
+static void comp_algorithm_set(struct zram *zram, u32 idx, const char *alg)
+{
+	/* Do not kfree() algs that we didn't allocate, IOW the default ones */
+	if (zram->comp_algs[idx] != default_compressor)
+		kfree(zram->comp_algs[idx]);
+	zram->comp_algs[idx] = alg;
+}
+
 static ssize_t comp_algorithm_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
 	struct zram *zram = dev_to_zram(dev);
-	char compressor[ARRAY_SIZE(zram->compressor)];
+	char *compressor;
 	size_t sz;
 
-	strscpy(compressor, buf, sizeof(compressor));
+	sz = strlen(buf);
+	if (sz >= CRYPTO_MAX_ALG_NAME)
+		return -E2BIG;
+
+	compressor = kstrdup(buf, GFP_KERNEL);
+	if (!compressor)
+		return -ENOMEM;
+
 	/* ignore trailing newline */
-	sz = strlen(compressor);
 	if (sz > 0 && compressor[sz - 1] == '\n')
 		compressor[sz - 1] = 0x00;
 
-	if (!zcomp_available_algorithm(compressor))
+	if (!zcomp_available_algorithm(compressor)) {
+		kfree(compressor);
 		return -EINVAL;
+	}
 
 	down_write(&zram->init_lock);
 	if (init_done(zram)) {
 		up_write(&zram->init_lock);
+		kfree(compressor);
 		pr_info("Can't change algorithm for initialized device\n");
 		return -EBUSY;
 	}
 
-	strcpy(zram->compressor, compressor);
+	comp_algorithm_set(zram, ZRAM_PRIMARY_ZCOMP, compressor);
 	up_write(&zram->init_lock);
 	return len;
 }
@@ -1284,7 +1301,7 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 	size = zram_get_obj_size(zram, index);
 
 	if (size != PAGE_SIZE)
-		zstrm = zcomp_stream_get(zram->comp);
+		zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_ZCOMP]);
 
 	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
 	if (size == PAGE_SIZE) {
@@ -1296,7 +1313,7 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 		dst = kmap_atomic(page);
 		ret = zcomp_decompress(zstrm, src, size, dst);
 		kunmap_atomic(dst);
-		zcomp_stream_put(zram->comp);
+		zcomp_stream_put(zram->comps[ZRAM_PRIMARY_ZCOMP]);
 	}
 	zs_unmap_object(zram->mem_pool, handle);
 	zram_slot_unlock(zram, index);
@@ -1363,13 +1380,13 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 	kunmap_atomic(mem);
 
 compress_again:
-	zstrm = zcomp_stream_get(zram->comp);
+	zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_ZCOMP]);
 	src = kmap_atomic(page);
 	ret = zcomp_compress(zstrm, src, &comp_len);
 	kunmap_atomic(src);
 
 	if (unlikely(ret)) {
-		zcomp_stream_put(zram->comp);
+		zcomp_stream_put(zram->comps[ZRAM_PRIMARY_ZCOMP]);
 		pr_err("Compression failed! err=%d\n", ret);
 		zs_free(zram->mem_pool, handle);
 		return ret;
@@ -1397,7 +1414,7 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 				__GFP_HIGHMEM |
 				__GFP_MOVABLE);
 	if (IS_ERR((void *)handle)) {
-		zcomp_stream_put(zram->comp);
+		zcomp_stream_put(zram->comps[ZRAM_PRIMARY_ZCOMP]);
 		atomic64_inc(&zram->stats.writestall);
 		handle = zs_malloc(zram->mem_pool, comp_len,
 				GFP_NOIO | __GFP_HIGHMEM |
@@ -1414,14 +1431,14 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 		 * zstrm buffer back. It is necessary that the dereferencing
 		 * of the zstrm variable below occurs correctly.
 		 */
-		zstrm = zcomp_stream_get(zram->comp);
+		zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_ZCOMP]);
 	}
 
 	alloced_pages = zs_get_total_pages(zram->mem_pool);
 	update_used_max(zram, alloced_pages);
 
 	if (zram->limit_pages && alloced_pages > zram->limit_pages) {
-		zcomp_stream_put(zram->comp);
+		zcomp_stream_put(zram->comps[ZRAM_PRIMARY_ZCOMP]);
 		zs_free(zram->mem_pool, handle);
 		return -ENOMEM;
 	}
@@ -1435,7 +1452,7 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 	if (comp_len == PAGE_SIZE)
 		kunmap_atomic(src);
 
-	zcomp_stream_put(zram->comp);
+	zcomp_stream_put(zram->comps[ZRAM_PRIMARY_ZCOMP]);
 	zs_unmap_object(zram->mem_pool, handle);
 	atomic64_add(comp_len, &zram->stats.compr_data_size);
 out:
@@ -1710,6 +1727,20 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
 	return ret;
 }
 
+static void zram_destroy_comps(struct zram *zram)
+{
+	u32 idx;
+
+	for (idx = 0; idx < ZRAM_MAX_ZCOMPS; idx++) {
+		struct zcomp *comp = zram->comps[idx];
+
+		zram->comps[idx] = NULL;
+		if (IS_ERR_OR_NULL(comp))
+			continue;
+		zcomp_destroy(comp);
+	}
+}
+
 static void zram_reset_device(struct zram *zram)
 {
 	down_write(&zram->init_lock);
@@ -1727,11 +1758,11 @@ static void zram_reset_device(struct zram *zram)
 	/* I/O operation under all of CPU are done so let's free */
 	zram_meta_free(zram, zram->disksize);
 	zram->disksize = 0;
+	zram_destroy_comps(zram);
 	memset(&zram->stats, 0, sizeof(zram->stats));
-	zcomp_destroy(zram->comp);
-	zram->comp = NULL;
 	reset_bdev(zram);
 
+	comp_algorithm_set(zram, ZRAM_PRIMARY_ZCOMP, default_compressor);
 	up_write(&zram->init_lock);
 }
 
@@ -1742,6 +1773,7 @@ static ssize_t disksize_store(struct device *dev,
 	struct zcomp *comp;
 	struct zram *zram = dev_to_zram(dev);
 	int err;
+	u32 idx;
 
 	disksize = memparse(buf, NULL);
 	if (!disksize)
@@ -1760,22 +1792,25 @@ static ssize_t disksize_store(struct device *dev,
 		goto out_unlock;
 	}
 
-	comp = zcomp_create(zram->compressor);
-	if (IS_ERR(comp)) {
-		pr_err("Cannot initialise %s compressing backend\n",
-				zram->compressor);
-		err = PTR_ERR(comp);
-		goto out_free_meta;
-	}
+	for (idx = 0; idx < ZRAM_MAX_ZCOMPS; idx++) {
+		comp = zcomp_create(zram->comp_algs[idx]);
+		if (IS_ERR(comp)) {
+			pr_err("Cannot initialise %s compressing backend\n",
+			       zram->comp_algs[idx]);
+			err = PTR_ERR(comp);
+			goto out_free_comps;
+		}
 
-	zram->comp = comp;
+		zram->comps[idx] = comp;
+	}
 	zram->disksize = disksize;
 	set_capacity_and_notify(zram->disk, zram->disksize >> SECTOR_SHIFT);
 	up_write(&zram->init_lock);
 
 	return len;
 
-out_free_meta:
+out_free_comps:
+	zram_destroy_comps(zram);
 	zram_meta_free(zram, disksize);
 out_unlock:
 	up_write(&zram->init_lock);
@@ -1962,7 +1997,7 @@ static int zram_add(void)
 	if (ret)
 		goto out_cleanup_disk;
 
-	strscpy(zram->compressor, default_compressor, sizeof(zram->compressor));
+	zram->comp_algs[ZRAM_PRIMARY_ZCOMP] = default_compressor;
 
 	zram_debugfs_register(zram);
 	pr_info("Added device: %s\n", zram->disk->disk_name);
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index a2bda53020fd..4044ddbb2326 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -89,10 +89,20 @@ struct zram_stats {
 #endif
 };
 
+#ifdef CONFIG_ZRAM_MULTI_COMP
+#define ZRAM_PRIMARY_ZCOMP	0
+#define ZRAM_SECONDARY_ZCOMP	1
+#define ZRAM_MAX_ZCOMPS	2
+#else
+#define ZRAM_PRIMARY_ZCOMP	0
+#define ZRAM_SECONDARY_ZCOMP	0
+#define ZRAM_MAX_ZCOMPS	1
+#endif
+
 struct zram {
 	struct zram_table_entry *table;
 	struct zs_pool *mem_pool;
-	struct zcomp *comp;
+	struct zcomp *comps[ZRAM_MAX_ZCOMPS];
 	struct gendisk *disk;
 	/* Prevent concurrent execution of device init */
 	struct rw_semaphore init_lock;
@@ -107,7 +117,7 @@ struct zram {
 	 * we can store in a disk.
 	 */
 	u64 disksize;	/* bytes */
-	char compressor[CRYPTO_MAX_ALG_NAME];
+	const char *comp_algs[ZRAM_MAX_ZCOMPS];
 	/*
 	 * zram is claimed so open request will be failed
 	 */
-- 
2.38.0.rc1.362.ged0d419d3c-goog

[PATCHv3 2/8] zram: Add recompression algorithm sysfs knob

[Sergey Senozhatsky]

Introduce recomp_algorithm sysfs knob that controls
secondary algorithm selection used for recompression.
This device attribute works in a similar way with
comp_algorithm attribute.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 111 +++++++++++++++++++++++++++-------
 1 file changed, 90 insertions(+), 21 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 770ea3489eb6..a8ef3c0c3dae 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -41,7 +41,12 @@ static DEFINE_IDR(zram_index_idr);
 static DEFINE_MUTEX(zram_index_mutex);
 
 static int zram_major;
-static const char *default_compressor = CONFIG_ZRAM_DEF_COMP;
+static const char *default_comp_algs[ZRAM_MAX_ZCOMPS] = {
+	CONFIG_ZRAM_DEF_COMP,
+#ifdef CONFIG_ZRAM_MULTI_COMP
+	"zstd",
+#endif
+};
 
 /* Module params (documentation at end) */
 static unsigned int num_devices = 1;
@@ -1000,31 +1005,37 @@ static ssize_t max_comp_streams_store(struct device *dev,
 	return len;
 }
 
-static ssize_t comp_algorithm_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
+static void comp_algorithm_set(struct zram *zram, u32 idx, const char *alg)
 {
-	size_t sz;
-	struct zram *zram = dev_to_zram(dev);
+	bool default_alg = false;
+	int i;
 
-	down_read(&zram->init_lock);
-	sz = zcomp_available_show(zram->comp_algs[ZRAM_PRIMARY_ZCOMP], buf);
-	up_read(&zram->init_lock);
+	/* Do not kfree() algs that we didn't allocate, IOW the default ones */
+	for (i = 0; i < ZRAM_MAX_ZCOMPS; i++) {
+		if (zram->comp_algs[idx] == default_comp_algs[i]) {
+			default_alg = true;
+			break;
+		}
+	}
 
-	return sz;
+	if (!default_alg)
+		kfree(zram->comp_algs[idx]);
+	zram->comp_algs[idx] = alg;
 }
 
-static void comp_algorithm_set(struct zram *zram, u32 idx, const char *alg)
+static ssize_t __comp_algorithm_show(struct zram *zram, u32 idx, char *buf)
 {
-	/* Do not kfree() algs that we didn't allocate, IOW the default ones */
-	if (zram->comp_algs[idx] != default_compressor)
-		kfree(zram->comp_algs[idx]);
-	zram->comp_algs[idx] = alg;
+	ssize_t sz;
+
+	down_read(&zram->init_lock);
+	sz = zcomp_available_show(zram->comp_algs[idx], buf);
+	up_read(&zram->init_lock);
+
+	return sz;
 }
 
-static ssize_t comp_algorithm_store(struct device *dev,
-		struct device_attribute *attr, const char *buf, size_t len)
+static int __comp_algorithm_store(struct zram *zram, u32 idx, const char *buf)
 {
-	struct zram *zram = dev_to_zram(dev);
 	char *compressor;
 	size_t sz;
 
@@ -1053,11 +1064,55 @@ static ssize_t comp_algorithm_store(struct device *dev,
 		return -EBUSY;
 	}
 
-	comp_algorithm_set(zram, ZRAM_PRIMARY_ZCOMP, compressor);
+	comp_algorithm_set(zram, idx, compressor);
 	up_write(&zram->init_lock);
-	return len;
+	return 0;
+}
+
+static ssize_t comp_algorithm_show(struct device *dev,
+				   struct device_attribute *attr,
+				   char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+
+	return __comp_algorithm_show(zram, ZRAM_PRIMARY_ZCOMP, buf);
+}
+
+static ssize_t comp_algorithm_store(struct device *dev,
+				    struct device_attribute *attr,
+				    const char *buf,
+				    size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	int ret;
+
+	ret = __comp_algorithm_store(zram, ZRAM_PRIMARY_ZCOMP, buf);
+	return ret ? ret : len;
 }
 
+#ifdef CONFIG_ZRAM_MULTI_COMP
+static ssize_t recomp_algorithm_show(struct device *dev,
+				     struct device_attribute *attr,
+				     char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+
+	return __comp_algorithm_show(zram, ZRAM_SECONDARY_ZCOMP, buf);
+}
+
+static ssize_t recomp_algorithm_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf,
+				      size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	int ret;
+
+	ret = __comp_algorithm_store(zram, ZRAM_SECONDARY_ZCOMP, buf);
+	return ret ? ret : len;
+}
+#endif
+
 static ssize_t compact_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
@@ -1762,7 +1817,11 @@ static void zram_reset_device(struct zram *zram)
 	memset(&zram->stats, 0, sizeof(zram->stats));
 	reset_bdev(zram);
 
-	comp_algorithm_set(zram, ZRAM_PRIMARY_ZCOMP, default_compressor);
+	comp_algorithm_set(zram, ZRAM_PRIMARY_ZCOMP,
+			   default_comp_algs[ZRAM_PRIMARY_ZCOMP]);
+	if (IS_ENABLED(CONFIG_ZRAM_MULTI_COMP))
+		comp_algorithm_set(zram, ZRAM_SECONDARY_ZCOMP,
+				   default_comp_algs[ZRAM_SECONDARY_ZCOMP]);
 	up_write(&zram->init_lock);
 }
 
@@ -1895,6 +1954,9 @@ static DEVICE_ATTR_WO(writeback);
 static DEVICE_ATTR_RW(writeback_limit);
 static DEVICE_ATTR_RW(writeback_limit_enable);
 #endif
+#ifdef CONFIG_ZRAM_MULTI_COMP
+static DEVICE_ATTR_RW(recomp_algorithm);
+#endif
 
 static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_disksize.attr,
@@ -1918,6 +1980,9 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_bd_stat.attr,
 #endif
 	&dev_attr_debug_stat.attr,
+#ifdef CONFIG_ZRAM_MULTI_COMP
+	&dev_attr_recomp_algorithm.attr,
+#endif
 	NULL,
 };
 
@@ -1997,7 +2062,11 @@ static int zram_add(void)
 	if (ret)
 		goto out_cleanup_disk;
 
-	zram->comp_algs[ZRAM_PRIMARY_ZCOMP] = default_compressor;
+	zram->comp_algs[ZRAM_PRIMARY_ZCOMP] =
+		default_comp_algs[ZRAM_PRIMARY_ZCOMP];
+	if (IS_ENABLED(CONFIG_ZRAM_MULTI_COMP))
+		zram->comp_algs[ZRAM_SECONDARY_ZCOMP] =
+			default_comp_algs[ZRAM_SECONDARY_ZCOMP];
 
 	zram_debugfs_register(zram);
 	pr_info("Added device: %s\n", zram->disk->disk_name);
-- 
2.38.0.rc1.362.ged0d419d3c-goog

[PATCHv3 3/8] zram: Factor out WB and non-WB zram read functions

[Sergey Senozhatsky]

We will use non-WB variant in ZRAM page recompression path.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 73 ++++++++++++++++++++++++-----------
 1 file changed, 50 insertions(+), 23 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index a8ef3c0c3dae..94c62d7ea818 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1314,8 +1314,30 @@ static void zram_free_page(struct zram *zram, size_t index)
 		~(1UL << ZRAM_LOCK | 1UL << ZRAM_UNDER_WB));
 }
 
-static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
-				struct bio *bio, bool partial_io)
+/*
+ * Reads a page from the writeback devices. Corresponding ZRAM slot
+ * should be unlocked.
+ */
+static int zram_read_from_writeback(struct zram *zram, struct page *page,
+				    u32 index, struct bio *bio,
+				    bool partial_io)
+{
+	struct bio_vec bvec;
+
+	bvec.bv_page = page;
+	bvec.bv_len = PAGE_SIZE;
+	bvec.bv_offset = 0;
+	return read_from_bdev(zram, &bvec,
+			      zram_get_element(zram, index),
+			      bio, partial_io);
+}
+
+/*
+ * Reads (decompresses if needed) a page from zspool (zsmalloc).
+ * Corresponding ZRAM slot should be locked.
+ */
+static int zram_read_from_zspool(struct zram *zram, struct page *page,
+				 u32 index)
 {
 	struct zcomp_strm *zstrm;
 	unsigned long handle;
@@ -1323,23 +1345,6 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 	void *src, *dst;
 	int ret;
 
-	zram_slot_lock(zram, index);
-	if (zram_test_flag(zram, index, ZRAM_WB)) {
-		struct bio_vec bvec;
-
-		zram_slot_unlock(zram, index);
-		/* A null bio means rw_page was used, we must fallback to bio */
-		if (!bio)
-			return -EOPNOTSUPP;
-
-		bvec.bv_page = page;
-		bvec.bv_len = PAGE_SIZE;
-		bvec.bv_offset = 0;
-		return read_from_bdev(zram, &bvec,
-				zram_get_element(zram, index),
-				bio, partial_io);
-	}
-
 	handle = zram_get_handle(zram, index);
 	if (!handle || zram_test_flag(zram, index, ZRAM_SAME)) {
 		unsigned long value;
@@ -1349,7 +1354,6 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 		mem = kmap_atomic(page);
 		zram_fill_page(mem, PAGE_SIZE, value);
 		kunmap_atomic(mem);
-		zram_slot_unlock(zram, index);
 		return 0;
 	}
 
@@ -1371,17 +1375,40 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 		zcomp_stream_put(zram->comps[ZRAM_PRIMARY_ZCOMP]);
 	}
 	zs_unmap_object(zram->mem_pool, handle);
-	zram_slot_unlock(zram, index);
+	return ret;
+}
+
+static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
+			    struct bio *bio, bool partial_io)
+{
+	int ret;
+
+	zram_slot_lock(zram, index);
+	if (!zram_test_flag(zram, index, ZRAM_WB)) {
+		/* Slot should be locked through out the function call */
+		ret = zram_read_from_zspool(zram, page, index);
+		zram_slot_unlock(zram, index);
+	} else {
+		/* Slot should be unlocked before the function call */
+		zram_slot_unlock(zram, index);
+
+		/* A null bio means rw_page was used, we must fallback to bio */
+		if (!bio)
+			return -EOPNOTSUPP;
+
+		ret = zram_read_from_writeback(zram, page, index, bio,
+					       partial_io);
+	}
 
 	/* Should NEVER happen. Return bio error if it does. */
-	if (WARN_ON(ret))
+	if (WARN_ON(ret < 0))
 		pr_err("Decompression failed! err=%d, page=%u\n", ret, index);
 
 	return ret;
 }
 
 static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
-				u32 index, int offset, struct bio *bio)
+			  u32 index, int offset, struct bio *bio)
 {
 	int ret;
 	struct page *page;
-- 
2.38.0.rc1.362.ged0d419d3c-goog

[PATCHv3 4/8] zram: Introduce recompress sysfs knob

[Sergey Senozhatsky]

Allow zram to recompress (using secondary compression streams)
pages. We support three modes:

1) IDLE pages recompression is activated by `idle` mode

	echo idle > /sys/block/zram0/recompress

2) Since there may be many idle pages user-space may pass a size
watermark value and we will recompress IDLE pages only of equal
or greater size:

	echo 888 > /sys/block/zram0/recompress

3) HUGE pages recompression is activated by `huge` mode

	echo huge > /sys/block/zram0/recompress

4) HUGE_IDLE pages recompression is activated by `huge_idle` mode

	echo huge_idle > /sys/block/zram0/recompress

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/Kconfig    |  12 +++
 drivers/block/zram/zram_drv.c | 194 +++++++++++++++++++++++++++++++++-
 drivers/block/zram/zram_drv.h |   2 +
 3 files changed, 205 insertions(+), 3 deletions(-)

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index d4100b0c083e..7febf36e93eb 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -78,3 +78,15 @@ config ZRAM_MEMORY_TRACKING
 	  /sys/kernel/debug/zram/zramX/block_state.
 
 	  See Documentation/admin-guide/blockdev/zram.rst for more information.
+
+config ZRAM_MULTI_COMP
+	bool "Enable multiple per-CPU compression streams"
+	depends on ZRAM
+	help
+	This will enable per-CPU multi-compression streams, so that ZRAM
+	can re-compress IDLE/huge pages, using a potentially slower but
+	more effective compression algorithm. Note, that IDLE page support
+	requires ZRAM_MEMORY_TRACKING.
+
+          echo TIMEOUT > /sys/block/zramX/idle
+          echo SIZE > /sys/block/zramX/recompress
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 94c62d7ea818..12368e773f3d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1282,6 +1282,12 @@ static void zram_free_page(struct zram *zram, size_t index)
 		atomic64_dec(&zram->stats.huge_pages);
 	}
 
+	if (zram_test_flag(zram, index, ZRAM_RECOMP))
+		zram_clear_flag(zram, index, ZRAM_RECOMP);
+
+	if (zram_test_flag(zram, index, ZRAM_RECOMP_SKIP))
+		zram_clear_flag(zram, index, ZRAM_RECOMP_SKIP);
+
 	if (zram_test_flag(zram, index, ZRAM_WB)) {
 		zram_clear_flag(zram, index, ZRAM_WB);
 		free_block_bdev(zram, zram_get_element(zram, index));
@@ -1343,6 +1349,7 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
 	unsigned long handle;
 	unsigned int size;
 	void *src, *dst;
+	u32 idx;
 	int ret;
 
 	handle = zram_get_handle(zram, index);
@@ -1359,8 +1366,13 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
 
 	size = zram_get_obj_size(zram, index);
 
-	if (size != PAGE_SIZE)
-		zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_ZCOMP]);
+	if (size != PAGE_SIZE) {
+		idx = ZRAM_PRIMARY_ZCOMP;
+		if (zram_test_flag(zram, index, ZRAM_RECOMP))
+			idx = ZRAM_SECONDARY_ZCOMP;
+
+		zstrm = zcomp_stream_get(zram->comps[idx]);
+	}
 
 	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
 	if (size == PAGE_SIZE) {
@@ -1372,7 +1384,7 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
 		dst = kmap_atomic(page);
 		ret = zcomp_decompress(zstrm, src, size, dst);
 		kunmap_atomic(dst);
-		zcomp_stream_put(zram->comps[ZRAM_PRIMARY_ZCOMP]);
+		zcomp_stream_put(zram->comps[idx]);
 	}
 	zs_unmap_object(zram->mem_pool, handle);
 	return ret;
@@ -1603,6 +1615,180 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 	return ret;
 }
 
+#ifdef CONFIG_ZRAM_MULTI_COMP
+/*
+ * This function will decompress (unless it's ZRAM_HUGE) the page and then
+ * attempt to compress it using secondary compression algorithm (which is
+ * potentially more effective).
+ *
+ * Corresponding ZRAM slot should be locked.
+ */
+static int zram_recompress(struct zram *zram,
+			   u32 index,
+			   struct page *page,
+			   int size_watermark)
+{
+	unsigned long handle_prev;
+	unsigned long handle_next;
+	unsigned int comp_len_next;
+	unsigned int  comp_len_prev;
+	struct zcomp_strm *zstrm;
+	void *src, *dst;
+	int ret;
+
+	handle_prev = zram_get_handle(zram, index);
+	if (!handle_prev)
+		return -EINVAL;
+
+	comp_len_prev = zram_get_obj_size(zram, index);
+	/*
+	 * Do not recompress objects that are already "small enough".
+	 */
+	if (comp_len_prev < size_watermark)
+		return 0;
+
+	ret = zram_read_from_zspool(zram, page, index);
+	if (ret)
+		return ret;
+
+	zstrm = zcomp_stream_get(zram->comps[ZRAM_SECONDARY_ZCOMP]);
+	src = kmap_atomic(page);
+	ret = zcomp_compress(zstrm, src, &comp_len_next);
+	kunmap_atomic(src);
+
+	/*
+	 * Either a compression error or we failed to compressed the object
+	 * in a way that will save us memory. Mark the object so that we
+	 * don't attemp to re-compress it again (RECOMP_SKIP).
+	 */
+	if (comp_len_next >= huge_class_size ||
+	    comp_len_next >= comp_len_prev ||
+	    ret) {
+		zram_set_flag(zram, index, ZRAM_RECOMP_SKIP);
+		zram_clear_flag(zram, index, ZRAM_IDLE);
+		zcomp_stream_put(zram->comps[ZRAM_SECONDARY_ZCOMP]);
+		return ret;
+	}
+
+	/*
+	 * No direct reclaim (slow path) for handle allocation and no
+	 * re-compression attempt (unlike in __zram_bvec_write()) since
+	 * we already stored that object in zsmalloc. If we cannot alloc
+	 * memory then me bail out.
+	 */
+	handle_next = zs_malloc(zram->mem_pool, comp_len_next,
+				__GFP_KSWAPD_RECLAIM |
+				__GFP_NOWARN |
+				__GFP_HIGHMEM |
+				__GFP_MOVABLE);
+	if (IS_ERR((void *)handle_next)) {
+		zcomp_stream_put(zram->comps[ZRAM_SECONDARY_ZCOMP]);
+		return -ENOMEM;
+	}
+
+	dst = zs_map_object(zram->mem_pool, handle_next, ZS_MM_WO);
+	memcpy(dst, zstrm->buffer, comp_len_next);
+	zcomp_stream_put(zram->comps[ZRAM_SECONDARY_ZCOMP]);
+
+	zs_unmap_object(zram->mem_pool, handle_next);
+
+	zram_free_page(zram, index);
+	zram_set_handle(zram, index, handle_next);
+	zram_set_obj_size(zram, index, comp_len_next);
+
+	zram_set_flag(zram, index, ZRAM_RECOMP);
+	atomic64_add(comp_len_next, &zram->stats.compr_data_size);
+	atomic64_inc(&zram->stats.pages_stored);
+
+	return 0;
+}
+
+#define RECOMPRESS_IDLE		(1 << 0)
+#define RECOMPRESS_HUGE		(1 << 1)
+
+static ssize_t recompress_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf,
+				size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
+	unsigned long index;
+	struct page *page;
+	ssize_t ret = 0;
+	int mode, size_watermark = 0;
+
+	if (sysfs_streq(buf, "idle")) {
+		mode = RECOMPRESS_IDLE;
+	} else if (sysfs_streq(buf, "huge")) {
+		mode = RECOMPRESS_HUGE;
+	} else if (sysfs_streq(buf, "huge_idle")) {
+		mode = RECOMPRESS_IDLE | RECOMPRESS_HUGE;
+	} else {
+		/*
+		 * We will re-compress only idle objects equal or greater
+		 * in size than watermark.
+		 */
+		ret = kstrtoint(buf, 10, &size_watermark);
+		if (ret)
+			return ret;
+		mode = RECOMPRESS_IDLE;
+	}
+
+	if (size_watermark > PAGE_SIZE)
+		return ret;
+
+	down_read(&zram->init_lock);
+	if (!init_done(zram)) {
+		ret = -EINVAL;
+		goto release_init_lock;
+	}
+
+	page = alloc_page(GFP_KERNEL);
+	if (!page) {
+		ret = -ENOMEM;
+		goto release_init_lock;
+	}
+
+	for (index = 0; index < nr_pages; index++) {
+		zram_slot_lock(zram, index);
+
+		if (!zram_allocated(zram, index))
+			goto next;
+
+		if (mode & RECOMPRESS_IDLE &&
+		    !zram_test_flag(zram, index, ZRAM_IDLE))
+			goto next;
+
+		if (mode & RECOMPRESS_HUGE &&
+		    !zram_test_flag(zram, index, ZRAM_HUGE))
+			goto next;
+
+		if (zram_test_flag(zram, index, ZRAM_WB) ||
+		    zram_test_flag(zram, index, ZRAM_UNDER_WB) ||
+		    zram_test_flag(zram, index, ZRAM_SAME) ||
+		    zram_test_flag(zram, index, ZRAM_RECOMP) ||
+		    zram_test_flag(zram, index, ZRAM_RECOMP_SKIP))
+			goto next;
+
+		ret = zram_recompress(zram, index, page, size_watermark);
+next:
+		zram_slot_unlock(zram, index);
+		if (ret)
+			break;
+
+		cond_resched();
+	}
+
+	ret = len;
+	__free_page(page);
+
+release_init_lock:
+	up_read(&zram->init_lock);
+	return ret;
+}
+#endif
+
 /*
  * zram_bio_discard - handler on discard request
  * @index: physical block index in PAGE_SIZE units
@@ -1983,6 +2169,7 @@ static DEVICE_ATTR_RW(writeback_limit_enable);
 #endif
 #ifdef CONFIG_ZRAM_MULTI_COMP
 static DEVICE_ATTR_RW(recomp_algorithm);
+static DEVICE_ATTR_WO(recompress);
 #endif
 
 static struct attribute *zram_disk_attrs[] = {
@@ -2009,6 +2196,7 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_debug_stat.attr,
 #ifdef CONFIG_ZRAM_MULTI_COMP
 	&dev_attr_recomp_algorithm.attr,
+	&dev_attr_recompress.attr,
 #endif
 	NULL,
 };
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 4044ddbb2326..09b9ceb5dfa3 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -49,6 +49,8 @@ enum zram_pageflags {
 	ZRAM_UNDER_WB,	/* page is under writeback */
 	ZRAM_HUGE,	/* Incompressible page */
 	ZRAM_IDLE,	/* not accessed page since last idle marking */
+	ZRAM_RECOMP,	/* page was recompressed */
+	ZRAM_RECOMP_SKIP, /* secondary algorithm cannot compress this page */
 
 	__NR_ZRAM_PAGEFLAGS,
 };
-- 
2.38.0.rc1.362.ged0d419d3c-goog

Re: [PATCHv3 4/8] zram: Introduce recompress sysfs knob

[Andrew Morton]

On Sun,  9 Oct 2022 18:07:16 +0900 Sergey Senozhatsky <senozhatsky@chromium.org> wrote:

> Allow zram to recompress (using secondary compression streams)
> pages. We support three modes:
> 
> 1) IDLE pages recompression is activated by `idle` mode
> 
> 	echo idle > /sys/block/zram0/recompress
> 
> 2) Since there may be many idle pages user-space may pass a size
> watermark value and we will recompress IDLE pages only of equal
> or greater size:
> 
> 	echo 888 > /sys/block/zram0/recompress

It's helpful to describe the units ("bytes") here and in the
docmentation.

> 3) HUGE pages recompression is activated by `huge` mode
> 
> 	echo huge > /sys/block/zram0/recompress
> 
> 4) HUGE_IDLE pages recompression is activated by `huge_idle` mode
> 
> 	echo huge_idle > /sys/block/zram0/recompress
> 
> ...
>
> +	if (IS_ERR((void *)handle_next)) {

IS_ERR_VALUE() avoids castsing back and forth.

Re: [PATCHv3 4/8] zram: Introduce recompress sysfs knob

[Sergey Senozhatsky]

On (22/10/17 17:08), Andrew Morton wrote:
> > Allow zram to recompress (using secondary compression streams)
> > pages. We support three modes:
> > 
> > 1) IDLE pages recompression is activated by `idle` mode
> > 
> > 	echo idle > /sys/block/zram0/recompress
> > 
> > 2) Since there may be many idle pages user-space may pass a size
> > watermark value and we will recompress IDLE pages only of equal
> > or greater size:
> > 
> > 	echo 888 > /sys/block/zram0/recompress
> 
> It's helpful to describe the units ("bytes") here and in the
> docmentation.

Will send fixup patches.

> > 3) HUGE pages recompression is activated by `huge` mode
> > 
> > 	echo huge > /sys/block/zram0/recompress
> > 
> > 4) HUGE_IDLE pages recompression is activated by `huge_idle` mode
> > 
> > 	echo huge_idle > /sys/block/zram0/recompress
> > 
> > ...
> >
> > +	if (IS_ERR((void *)handle_next)) {
> 
> IS_ERR_VALUE() avoids castsing back and forth.

Thanks, I'll send a separate patch for this (if you don't mind).

Re: [PATCHv3 4/8] zram: Introduce recompress sysfs knob

[Sergey Senozhatsky]

A fixup patch: update Kconfig description and tweak coding styles.

---

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index 7febf36e93eb..3e00656a6f8a 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -90,3 +90,6 @@ config ZRAM_MULTI_COMP
 
           echo TIMEOUT > /sys/block/zramX/idle
           echo SIZE > /sys/block/zramX/recompress
+
+	SIZE (in bytes) parameter sets the object size watermark: idle
+	objects that are of a smaller size will not get recompressed.
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 12368e773f3d..143c33bd6783 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1623,9 +1623,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
  *
  * Corresponding ZRAM slot should be locked.
  */
-static int zram_recompress(struct zram *zram,
-			   u32 index,
-			   struct page *page,
+static int zram_recompress(struct zram *zram, u32 index, struct page *page,
 			   int size_watermark)
 {
 	unsigned long handle_prev;
@@ -1708,8 +1706,7 @@ static int zram_recompress(struct zram *zram,
 
 static ssize_t recompress_store(struct device *dev,
 				struct device_attribute *attr,
-				const char *buf,
-				size_t len)
+				const char *buf, size_t len)
 {
 	struct zram *zram = dev_to_zram(dev);
 	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;

[PATCHv3 5/8] documentation: Add recompression documentation

[Sergey Senozhatsky]

Document user-space visible device attributes that
are enabled by ZRAM_MULTI_COMP.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 Documentation/admin-guide/blockdev/zram.rst | 55 +++++++++++++++++++++
 drivers/block/zram/zram_drv.c               |  7 +--
 2 files changed, 57 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index c73b16930449..88957fcb6ad7 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -401,6 +401,61 @@ budget in next setting is user's job.
 If admin wants to measure writeback count in a certain period, they could
 know it via /sys/block/zram0/bd_stat's 3rd column.
 
+recompression
+-------------
+
+With CONFIG_ZRAM_MULTI_COMP, zram can recompress idle/huge pages using
+alternative (secondary) compression algorithm. The basic idea is that
+alternative compression algorithm can provide better compression ratio
+at a price of (potentially) slower compression/decompression speeds.
+Alternative compression algorithm can, for example, be more successful
+compressing huge pages (those that default algorithm failed to compress).
+Another application is idle pages recompression - pages that are cold and
+sit in the memory can be recompressed using more effective algorithm and,
+hence, reduce zsmalloc memory usage.
+
+With CONFIG_ZRAM_MULTI_COMP, zram will setup two compression algorithms
+per-CPU: primary and secondary ones. Primary zram compressor is explained
+in "3) Select compression algorithm", the secondary algorithm is configured
+in a similar way, using recomp_algorithm device attribute:
+
+Examples::
+
+	#show supported recompression algorithms
+	cat /sys/block/zramX/recomp_algorithm
+	zstd [lzo]
+
+	#select zstd recompression algorithm
+	echo zstd > /sys/block/zramX/recomp_algorithm
+
+Another device attribute that CONFIG_ZRAM_MULTI_COMP enables is recompress,
+which controls recompression:
+
+Examples::
+
+	#IDLE pages recompression is activated by `idle` mode
+	echo idle > /sys/block/zramX/recompress
+
+	#HUGE pages recompression is activated by `huge` mode
+	echo huge > /sys/block/zram0/recompress
+
+	#HUGE_IDLE pages recompression is activated by `huge_idle` mode
+	echo huge_idle > /sys/block/zramX/recompress
+
+The number of idle pages can be significant, so user-space can pass a size
+watermark value to the recompress knob, to filter out idle pages for
+recompression: zram will recompress only idle pages of equal or greater
+size:::
+
+	#recompress idle pages larger than 3000 bytes
+	echo 3000 > /sys/block/zramX/recompress
+
+	#recompress idle pages larger than 2000 bytes
+	echo 2000 > /sys/block/zramX/recompress
+
+Recompression is mostly focused on idle pages (except for huge pages
+recompression), so it works better in conjunction with memory tracking.
+
 memory tracking
 ===============
 
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 12368e773f3d..143c33bd6783 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1623,9 +1623,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
  *
  * Corresponding ZRAM slot should be locked.
  */
-static int zram_recompress(struct zram *zram,
-			   u32 index,
-			   struct page *page,
+static int zram_recompress(struct zram *zram, u32 index, struct page *page,
 			   int size_watermark)
 {
 	unsigned long handle_prev;
@@ -1708,8 +1706,7 @@ static int zram_recompress(struct zram *zram,
 
 static ssize_t recompress_store(struct device *dev,
 				struct device_attribute *attr,
-				const char *buf,
-				size_t len)
+				const char *buf, size_t len)
 {
 	struct zram *zram = dev_to_zram(dev);
 	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
-- 
2.38.0.rc1.362.ged0d419d3c-goog

Re: [PATCHv3 5/8] documentation: Add recompression documentation

[Sergey Senozhatsky]

On (22/10/09 18:07), Sergey Senozhatsky wrote:
[..]
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 12368e773f3d..143c33bd6783 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1623,9 +1623,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
>   *
>   * Corresponding ZRAM slot should be locked.
>   */
> -static int zram_recompress(struct zram *zram,
> -			   u32 index,
> -			   struct page *page,
> +static int zram_recompress(struct zram *zram, u32 index, struct page *page,
>  			   int size_watermark)
>  {
>  	unsigned long handle_prev;
> @@ -1708,8 +1706,7 @@ static int zram_recompress(struct zram *zram,
>  
>  static ssize_t recompress_store(struct device *dev,
>  				struct device_attribute *attr,
> -				const char *buf,
> -				size_t len)
> +				const char *buf, size_t len)
>  {
>  	struct zram *zram = dev_to_zram(dev);
>  	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;

D'oh, this patch should not contain any code changes, only
documentation updates. It's the previous patch in the series
that should contain these coding-style tweaks. Rebasing did
not go spectacularly well here...

Andrew, what's the best way to handle this?

Re: [PATCHv3 5/8] documentation: Add recompression documentation

[Andrew Morton]

On Tue, 18 Oct 2022 11:22:25 +0900 Sergey Senozhatsky <senozhatsky@chromium.org> wrote:

> D'oh, this patch should not contain any code changes, only
> documentation updates. It's the previous patch in the series
> that should contain these coding-style tweaks. Rebasing did
> not go spectacularly well here...
> 
> Andrew, what's the best way to handle this?

May as well resend the whole patchset.

Re: [PATCHv3 5/8] documentation: Add recompression documentation

[Sergey Senozhatsky]

Document user-space visible device attributes that
are enabled by ZRAM_MULTI_COMP.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 Documentation/admin-guide/blockdev/zram.rst | 55 +++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index c73b16930449..f09e778bc3dc 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -401,6 +401,61 @@ budget in next setting is user's job.
 If admin wants to measure writeback count in a certain period, they could
 know it via /sys/block/zram0/bd_stat's 3rd column.
 
+recompression
+-------------
+
+With CONFIG_ZRAM_MULTI_COMP, zram can recompress idle/huge pages using
+alternative (secondary) compression algorithm. The basic idea is that
+alternative compression algorithm can provide better compression ratio
+at a price of (potentially) slower compression/decompression speeds.
+Alternative compression algorithm can, for example, be more successful
+compressing huge pages (those that default algorithm failed to compress).
+Another application is idle pages recompression - pages that are cold and
+sit in the memory can be recompressed using more effective algorithm and,
+hence, reduce zsmalloc memory usage.
+
+With CONFIG_ZRAM_MULTI_COMP, zram will setup two compression algorithms
+per-CPU: primary and secondary ones. Primary zram compressor is explained
+in "3) Select compression algorithm", the secondary algorithm is configured
+in a similar way, using recomp_algorithm device attribute:
+
+Examples::
+
+	#show supported recompression algorithms
+	cat /sys/block/zramX/recomp_algorithm
+	zstd [lzo]
+
+	#select zstd recompression algorithm
+	echo zstd > /sys/block/zramX/recomp_algorithm
+
+Another device attribute that CONFIG_ZRAM_MULTI_COMP enables is recompress,
+which controls recompression:
+
+Examples::
+
+	#IDLE pages recompression is activated by `idle` mode
+	echo idle > /sys/block/zramX/recompress
+
+	#HUGE pages recompression is activated by `huge` mode
+	echo huge > /sys/block/zram0/recompress
+
+	#HUGE_IDLE pages recompression is activated by `huge_idle` mode
+	echo huge_idle > /sys/block/zramX/recompress
+
+The number of idle pages can be significant, so user-space can pass a size
+watermark (in bytes) value to the recompress knob, to filter out idle pages
+for recompression: zram will recompress only idle pages of equal or greater
+size (bytes):::
+
+	#recompress idle pages larger than 3000 bytes
+	echo 3000 > /sys/block/zramX/recompress
+
+	#recompress idle pages larger than 2000 bytes
+	echo 2000 > /sys/block/zramX/recompress
+
+Recompression is mostly focused on idle pages (except for huge pages
+recompression), so it works better in conjunction with memory tracking.
+
 memory tracking
 ===============
 
-- 
2.38.0.413.g74048e4d9e-goog

[PATCHv3 6/8] zram: Add recompression algorithm choice to Kconfig

[Sergey Senozhatsky]

Make (secondary) recompression algorithm selectable just like
we do it for the (primary) default one.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/Kconfig    | 40 +++++++++++++++++++++++++++++++++++
 drivers/block/zram/zram_drv.c |  2 +-
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index 7febf36e93eb..442885ac72ca 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -90,3 +90,43 @@ config ZRAM_MULTI_COMP
 
           echo TIMEOUT > /sys/block/zramX/idle
           echo SIZE > /sys/block/zramX/recompress
+
+choice
+	prompt "Default zram recompression algorithm"
+	default ZRAM_DEF_RECOMP_ZSTD
+	depends on ZRAM && ZRAM_MULTI_COMP
+
+config ZRAM_DEF_RECOMP_LZORLE
+	bool "lzo-rle"
+	depends on CRYPTO_LZO
+
+config ZRAM_DEF_RECOMP_ZSTD
+	bool "zstd"
+	depends on CRYPTO_ZSTD
+
+config ZRAM_DEF_RECOMP_LZ4
+	bool "lz4"
+	depends on CRYPTO_LZ4
+
+config ZRAM_DEF_RECOMP_LZO
+	bool "lzo"
+	depends on CRYPTO_LZO
+
+config ZRAM_DEF_RECOMP_LZ4HC
+	bool "lz4hc"
+	depends on CRYPTO_LZ4HC
+
+config ZRAM_DEF_RECOMP_842
+	bool "842"
+	depends on CRYPTO_842
+
+endchoice
+
+config ZRAM_DEF_RECOMP
+	string
+	default "lzo-rle" if ZRAM_DEF_RECOMP_LZORLE
+	default "zstd" if ZRAM_DEF_RECOMP_ZSTD
+	default "lz4" if ZRAM_DEF_RECOMP_LZ4
+	default "lzo" if ZRAM_DEF_RECOMP_LZO
+	default "lz4hc" if ZRAM_DEF_RECOMP_LZ4HC
+	default "842" if ZRAM_DEF_RECOMP_842
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 143c33bd6783..7285a85b4054 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -44,7 +44,7 @@ static int zram_major;
 static const char *default_comp_algs[ZRAM_MAX_ZCOMPS] = {
 	CONFIG_ZRAM_DEF_COMP,
 #ifdef CONFIG_ZRAM_MULTI_COMP
-	"zstd",
+	CONFIG_ZRAM_DEF_RECOMP,
 #endif
 };
 
-- 
2.38.0.rc1.362.ged0d419d3c-goog

Re: [PATCHv3 6/8] zram: Add recompression algorithm choice to Kconfig

[Sergey Senozhatsky]

Make (secondary) recompression algorithm selectable just like
we do it for the (primary) default one.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/Kconfig | 40 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index 3e00656a6f8a..076a76cd1664 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -93,3 +93,43 @@ config ZRAM_MULTI_COMP
 
 	SIZE (in bytes) parameter sets the object size watermark: idle
 	objects that are of a smaller size will not get recompressed.
+
+choice
+	prompt "Default zram recompression algorithm"
+	default ZRAM_DEF_RECOMP_ZSTD
+	depends on ZRAM && ZRAM_MULTI_COMP
+
+config ZRAM_DEF_RECOMP_LZORLE
+	bool "lzo-rle"
+	depends on CRYPTO_LZO
+
+config ZRAM_DEF_RECOMP_ZSTD
+	bool "zstd"
+	depends on CRYPTO_ZSTD
+
+config ZRAM_DEF_RECOMP_LZ4
+	bool "lz4"
+	depends on CRYPTO_LZ4
+
+config ZRAM_DEF_RECOMP_LZO
+	bool "lzo"
+	depends on CRYPTO_LZO
+
+config ZRAM_DEF_RECOMP_LZ4HC
+	bool "lz4hc"
+	depends on CRYPTO_LZ4HC
+
+config ZRAM_DEF_RECOMP_842
+	bool "842"
+	depends on CRYPTO_842
+
+endchoice
+
+config ZRAM_DEF_RECOMP
+	string
+	default "lzo-rle" if ZRAM_DEF_RECOMP_LZORLE
+	default "zstd" if ZRAM_DEF_RECOMP_ZSTD
+	default "lz4" if ZRAM_DEF_RECOMP_LZ4
+	default "lzo" if ZRAM_DEF_RECOMP_LZO
+	default "lz4hc" if ZRAM_DEF_RECOMP_LZ4HC
+	default "842" if ZRAM_DEF_RECOMP_842
-- 
2.38.0.413.g74048e4d9e-goog

[PATCHv3 7/8] zram: Add recompress flag to read_block_state()

[Sergey Senozhatsky]

Add a new flag to zram block state that shows if the page
was recompressed (using alternative compression algorithm).

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 Documentation/admin-guide/blockdev/zram.rst | 9 ++++++---
 drivers/block/zram/zram_drv.c               | 5 +++--
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index 88957fcb6ad7..70a3d0243b45 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -466,9 +466,10 @@ pages of the process with*pagemap.
 If you enable the feature, you could see block state via
 /sys/kernel/debug/zram/zram0/block_state". The output is as follows::
 
-	  300    75.033841 .wh.
-	  301    63.806904 s...
-	  302    63.806919 ..hi
+	  300    75.033841 .wh..
+	  301    63.806904 s....
+	  302    63.806919 ..hi.
+	  303    62.801919 ....r
 
 First column
 	zram's block index.
@@ -485,6 +486,8 @@ Third column
 		huge page
 	i:
 		idle page
+	r:
+		recompressed page (secondary compression algorithm)
 
 First line of above example says 300th block is accessed at 75.033841sec
 and the block's state is huge so it is written back to the backing
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 7285a85b4054..34bb21691cee 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -925,13 +925,14 @@ static ssize_t read_block_state(struct file *file, char __user *buf,
 
 		ts = ktime_to_timespec64(zram->table[index].ac_time);
 		copied = snprintf(kbuf + written, count,
-			"%12zd %12lld.%06lu %c%c%c%c\n",
+			"%12zd %12lld.%06lu %c%c%c%c%c\n",
 			index, (s64)ts.tv_sec,
 			ts.tv_nsec / NSEC_PER_USEC,
 			zram_test_flag(zram, index, ZRAM_SAME) ? 's' : '.',
 			zram_test_flag(zram, index, ZRAM_WB) ? 'w' : '.',
 			zram_test_flag(zram, index, ZRAM_HUGE) ? 'h' : '.',
-			zram_test_flag(zram, index, ZRAM_IDLE) ? 'i' : '.');
+			zram_test_flag(zram, index, ZRAM_IDLE) ? 'i' : '.',
+			zram_test_flag(zram, index, ZRAM_RECOMP) ? 'r' : '.');
 
 		if (count <= copied) {
 			zram_slot_unlock(zram, index);
-- 
2.38.0.rc1.362.ged0d419d3c-goog

[PATCHv3 8/8] zram: correct typos

[Sergey Senozhatsky]

Trivial comment typos fixes.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 34bb21691cee..ecbc5963b5b8 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -759,7 +759,7 @@ static ssize_t writeback_store(struct device *dev,
 			zram_slot_unlock(zram, index);
 			/*
 			 * Return last IO error unless every IO were
-			 * not suceeded.
+			 * not succeeded.
 			 */
 			ret = err;
 			continue;
@@ -1658,7 +1658,7 @@ static int zram_recompress(struct zram *zram, u32 index, struct page *page,
 	/*
 	 * Either a compression error or we failed to compressed the object
 	 * in a way that will save us memory. Mark the object so that we
-	 * don't attemp to re-compress it again (RECOMP_SKIP).
+	 * don't attempt to re-compress it again (RECOMP_SKIP).
 	 */
 	if (comp_len_next >= huge_class_size ||
 	    comp_len_next >= comp_len_prev ||
-- 
2.38.0.rc1.362.ged0d419d3c-goog

Re: [PATCHv3 8/8] zram: correct typos

[Andrew Morton]

On Sun,  9 Oct 2022 18:07:20 +0900 Sergey Senozhatsky <senozhatsky@chromium.org> wrote:

> Trivial comment typos fixes.
> 
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -759,7 +759,7 @@ static ssize_t writeback_store(struct device *dev,
>  			zram_slot_unlock(zram, index);
>  			/*
>  			 * Return last IO error unless every IO were
> -			 * not suceeded.
> +			 * not succeeded.

That's a pretty awkward sentence.  Why not "unless every IO failed".

If that's indeed what we're doing here.  Sounds odd.  What do we return
if all IOs indeed failed?

Re: [PATCHv3 8/8] zram: correct typos

[Sergey Senozhatsky]

On (22/10/17 17:08), Andrew Morton wrote:
> On Sun,  9 Oct 2022 18:07:20 +0900 Sergey Senozhatsky <senozhatsky@chromium.org> wrote:
> 
> > Trivial comment typos fixes.
> > 
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -759,7 +759,7 @@ static ssize_t writeback_store(struct device *dev,
> >  			zram_slot_unlock(zram, index);
> >  			/*
> >  			 * Return last IO error unless every IO were
> > -			 * not suceeded.
> > +			 * not succeeded.
> 
> That's a pretty awkward sentence.  Why not "unless every IO failed".
> 
> If that's indeed what we're doing here.  Sounds odd.  What do we return
> if all IOs indeed failed?

Hmm, yes, I didn't consider re-phrasing this comment but we probably
should do so. What we have there is

	while (nr_pages_to_write--) {
		err = submit_bio_wait();
		if (err) {
			ret = err;
			continue;
		}
	}
	return ret;

zram objects are independent and bio errors on individual writes are
non-fatal, if we failed to write-back a zram object (page) we just
continue and try to write the next one; at the same time we need to
signal user-space that some of those writes failed (doesn't matter
which ones or how many). That loop used to look as follows (as far
as I can tell):

	while (nr_pages_to_write--) {
		ret = submit_bio_wait();
	}
	return ret;

Notice how `ret' would get overwritten all the time, so we if we had,
say, a successful submit_bio_wait, then an unsuccessful one and a
successful one again, we would lose the track of the bio error that
happened on the second iteration and will always return 0 to user-space.
*Unless* the last (or all) submit_bio_wait() also failed, in which case
`ret' would hold the correct error code.

Will something like this look less awkward to you?

---

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index ecbc5963b5b8..23f1655b7837 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -758,8 +758,12 @@ static ssize_t writeback_store(struct device *dev,
 			zram_clear_flag(zram, index, ZRAM_IDLE);
 			zram_slot_unlock(zram, index);
 			/*
-			 * Return last IO error unless every IO were
-			 * not succeeded.
+			 * BIO errors are not fatal, we continue and simply
+			 * attempt to writeback the remaining objects (pages).
+			 * At the same time we need to signal user-space that
+			 * some writes (at least one, but also could be all of
+			 * them) were not successful and we do so by returning
+			 * the most recent BIO error.
 			 */
 			ret = err;
 			continue;

Re: [PATCHv3 0/8] zram: Support multiple compression streams

[Sergey Senozhatsky]

Andrew, I will send a rebased (v4) series shortly. Please drop the
patches from your tree.