zram: propagate error to user

PATCH In review Minchan Kim 2 participants 6 messages Mar 7, 2014 – Mar 10, 2014

Subsystems (3)

Documentation Block layer zram

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Minchan Kim

author maintainer

2014-03-07 01:56 UTC #0 lore raw

PATCH 1/1 zram: propagate error to user

When we initialized zcomp with single, we couldn't change max_comp_streams without zram reset but current interface doesn't show any error to user and even it changes max_comp_streams's value without any effect so it would make user very confusing.

This patch prevents max_comp_streams's change when zcomp was initialized as single zcomp and emit the error to user(ex, echo).

Signed-off-by Minchan Kim <[email protected]>

---
 Documentation/blockdev/zram.txt |  9 +++++----
 drivers/block/zram/zcomp.c      | 10 +++++-----
 drivers/block/zram/zcomp.h      |  4 ++--
 drivers/block/zram/zram_drv.c   | 15 +++++++++++----
 4 files changed, 23 insertions(+), 15 deletions(-)

Documentation/blockdev/zram.txt +5 -4

index 2604ffed51db..0595c3f56ccf 100644
@@ -37,10 +37,11 @@ Note:
 In order to enable compression backend's multi stream support max_comp_streams
 must be initially set to desired concurrency level before ZRAM device
 initialisation. Once the device initialised as a single stream compression
-backend (max_comp_streams equals to 0) changing the value of max_comp_streams
-will not take any effect, because single stream compression backend implemented
-as a special case and does not support dynamic max_comp_streams. Only multi
-stream backend supports dynamic max_comp_streams adjustment.
+backend (max_comp_streams equals to 1), you will see error if you try to change
+the value of max_comp_streams because single stream compression backend
+implemented as a special case by lock overhead issue and does not support
+dynamic max_comp_streams. Only multi stream backend supports dynamic
+max_comp_streams adjustment.
 
 3) Select compression algorithm
 	Using comp_algorithm device attribute one can see available and

drivers/block/zram/zcomp.c +5 -5

index 92a83df40a27..15fe6a27781b 100644
@@ -152,7 +152,7 @@ static void zcomp_strm_multi_release(struct zcomp *comp, struct zcomp_strm *zstr
 }
 
 /* change max_strm limit */
-static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	struct zcomp_strm_multi *zs = comp->stream;
 	struct zcomp_strm *zstrm;

@@ -171,7 +171,7 @@ static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 		zs->avail_strm--;
 	}
 	spin_unlock(&zs->strm_lock);
-	return 0;
+	return true;
 }
 
 static void zcomp_strm_multi_destroy(struct zcomp *comp)

@@ -231,10 +231,10 @@ static void zcomp_strm_single_release(struct zcomp *comp,
 	mutex_unlock(&zs->strm_lock);
 }
 
-static int zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	/* zcomp_strm_single support only max_comp_streams == 1 */
-	return -ENOTSUPP;
+	return 0;
 }
 
 static void zcomp_strm_single_destroy(struct zcomp *comp)

@@ -283,7 +283,7 @@ ssize_t zcomp_available_show(const char *comp, char *buf)
 	return sz;
 }
 
-int zcomp_set_max_streams(struct zcomp *comp, int num_strm)
+bool zcomp_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	return comp->set_max_streams(comp, num_strm);
 }

drivers/block/zram/zcomp.h +2 -2

index 8b8997f8613b..c59d1fca72c0 100644
@@ -46,7 +46,7 @@ struct zcomp {
 
 	struct zcomp_strm *(*strm_find)(struct zcomp *comp);
 	void (*strm_release)(struct zcomp *comp, struct zcomp_strm *zstrm);
-	int (*set_max_streams)(struct zcomp *comp, int num_strm);
+	bool (*set_max_streams)(struct zcomp *comp, int num_strm);
 	void (*destroy)(struct zcomp *comp);
 };

@@ -64,5 +64,5 @@ int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
 int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
 		size_t src_len, unsigned char *dst);
 
-int zcomp_set_max_streams(struct zcomp *comp, int num_strm);
+bool zcomp_set_max_streams(struct zcomp *comp, int num_strm);
 #endif /* _ZCOMP_H_ */

drivers/block/zram/zram_drv.c +11 -4

index 7631ef0cbc41..eead9db9b100 100644
@@ -128,17 +128,24 @@ static ssize_t max_comp_streams_store(struct device *dev,
 	struct zram *zram = dev_to_zram(dev);
 
 	if (kstrtoint(buf, 0, &num))
-		return -EINVAL;
+		goto out;
 	if (num < 1)
-		return -EINVAL;
+		goto out;
+
 	down_write(&zram->init_lock);
 	if (init_done(zram)) {
-		if (zcomp_set_max_streams(zram->comp, num))
+		if (!zcomp_set_max_streams(zram->comp, num)) {
 			pr_info("Cannot change max compression streams\n");
+			goto out_unlock;
+		}
 	}
+
 	zram->max_comp_streams = num;
-	up_write(&zram->init_lock);
 	return len;
+out_unlock:
+	up_write(&zram->init_lock);
+out:
+	return -EINVAL;
 }
 
 static ssize_t comp_algorithm_show(struct device *dev,

Signature · 1 line

1.9.0

Sergey Senozhatsky

2014-03-07 09:24 UTC #1 lore raw

Quoted 59 lines · Minchan Kim

This patch prevents max_comp_streams's change when zcomp was initialized as single zcomp and emit the error to user(ex, echo).

Signed-off-by Minchan Kim <[email protected]>

---
 Documentation/blockdev/zram.txt |  9 +++++----
 drivers/block/zram/zcomp.c      | 10 +++++-----
 drivers/block/zram/zcomp.h      |  4 ++--
 drivers/block/zram/zram_drv.c   | 15 +++++++++++----
 4 files changed, 23 insertions(+), 15 deletions(-)

Documentation/blockdev/zram.txt +5 -4

index 2604ffed51db..0595c3f56ccf 100644
@@ -37,10 +37,11 @@ Note:
 In order to enable compression backend's multi stream support max_comp_streams
 must be initially set to desired concurrency level before ZRAM device
 initialisation. Once the device initialised as a single stream compression
-backend (max_comp_streams equals to 0) changing the value of max_comp_streams
-will not take any effect, because single stream compression backend implemented
-as a special case and does not support dynamic max_comp_streams. Only multi
-stream backend supports dynamic max_comp_streams adjustment.
+backend (max_comp_streams equals to 1), you will see error if you try to change
+the value of max_comp_streams because single stream compression backend
+implemented as a special case by lock overhead issue and does not support
+dynamic max_comp_streams. Only multi stream backend supports dynamic
+max_comp_streams adjustment.
 
 3) Select compression algorithm
 	Using comp_algorithm device attribute one can see available and

drivers/block/zram/zcomp.c +2 -2

index 92a83df40a27..15fe6a27781b 100644
@@ -152,7 +152,7 @@ static void zcomp_strm_multi_release(struct zcomp *comp, struct zcomp_strm *zstr
 }
 
 /* change max_strm limit */
-static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	struct zcomp_strm_multi *zs = comp->stream;
 	struct zcomp_strm *zstrm;

@@ -171,7 +171,7 @@ static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 		zs->avail_strm--;
 	}
 	spin_unlock(&zs->strm_lock);
-	return 0;
+	return true;
 }
 
 static void zcomp_strm_multi_destroy(struct zcomp *comp)

drivers/block/zram/zcomp.c static void zcomp_strm_single_release(struct zcomp *comp, · line 238

Quoted 10 lines

drivers/block/zram/zcomp.c +2 -2

@@ -231,10 +231,10 @@ static void zcomp_strm_single_release(struct zcomp *comp,
 	mutex_unlock(&zs->strm_lock);
 }
 
-static int zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	/* zcomp_strm_single support only max_comp_streams == 1 */
-	return -ENOTSUPP;
+	return 0;
 }

IMHO, -ENOTSUPP for unsupported operation fits better than `false'. yes, currently there are only two possible returns:
0 -- success
-ENOTSUPP - not supported operation

though, we can extend functions later and return additional codes, other than false' and true'.

for example, -E2BIG if user requested extremly large number of streams, like 5000 streams.

Quoted 45 lines

drivers/block/zram/zcomp.c +1 -1

 static void zcomp_strm_single_destroy(struct zcomp *comp)

@@ -283,7 +283,7 @@ ssize_t zcomp_available_show(const char *comp, char *buf)
 	return sz;
 }
 
-int zcomp_set_max_streams(struct zcomp *comp, int num_strm)
+bool zcomp_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	return comp->set_max_streams(comp, num_strm);
 }

drivers/block/zram/zcomp.h +2 -2

index 8b8997f8613b..c59d1fca72c0 100644
@@ -46,7 +46,7 @@ struct zcomp {
 
 	struct zcomp_strm *(*strm_find)(struct zcomp *comp);
 	void (*strm_release)(struct zcomp *comp, struct zcomp_strm *zstrm);
-	int (*set_max_streams)(struct zcomp *comp, int num_strm);
+	bool (*set_max_streams)(struct zcomp *comp, int num_strm);
 	void (*destroy)(struct zcomp *comp);
 };

@@ -64,5 +64,5 @@ int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
 int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
 		size_t src_len, unsigned char *dst);
 
-int zcomp_set_max_streams(struct zcomp *comp, int num_strm);
+bool zcomp_set_max_streams(struct zcomp *comp, int num_strm);
 #endif /* _ZCOMP_H_ */

drivers/block/zram/zram_drv.c +3 -2

index 7631ef0cbc41..eead9db9b100 100644
@@ -128,17 +128,24 @@ static ssize_t max_comp_streams_store(struct device *dev,
 	struct zram *zram = dev_to_zram(dev);
 
 	if (kstrtoint(buf, 0, &num))
-		return -EINVAL;
+		goto out;
 	if (num < 1)
-		return -EINVAL;
+		goto out;
+

drivers/block/zram/zram_drv.c static ssize_t max_comp_streams_store(struct device *dev, · line 143

Quoted 10 lines

drivers/block/zram/zram_drv.c +4 -1

 	down_write(&zram->init_lock);
 	if (init_done(zram)) {
-		if (zcomp_set_max_streams(zram->comp, num))
+		if (!zcomp_set_max_streams(zram->comp, num)) {
 			pr_info("Cannot change max compression streams\n");
+			goto out_unlock;
+		}
 	}
+
 	zram->max_comp_streams = num;

agree, better to avoid this for a single stream.

Quoted 12 lines

drivers/block/zram/zram_drv.c +4 -1

-	up_write(&zram->init_lock);
 	return len;
+out_unlock:
+	up_write(&zram->init_lock);
+out:
+	return -EINVAL;
 }
 
 static ssize_t comp_algorithm_show(struct device *dev,

Signature · 1 line

1.9.0

Minchan Kim

author maintainer

2014-03-07 09:51 UTC #2 lore raw

Hello Sergey!

Quoted 76 lines · Sergey Senozhatsky

Quoted 59 lines · Minchan Kim

This patch prevents max_comp_streams's change when zcomp was initialized as single zcomp and emit the error to user(ex, echo).

Signed-off-by Minchan Kim <[email protected]>

---
 Documentation/blockdev/zram.txt |  9 +++++----
 drivers/block/zram/zcomp.c      | 10 +++++-----
 drivers/block/zram/zcomp.h      |  4 ++--
 drivers/block/zram/zram_drv.c   | 15 +++++++++++----
 4 files changed, 23 insertions(+), 15 deletions(-)

Documentation/blockdev/zram.txt +5 -4

index 2604ffed51db..0595c3f56ccf 100644
@@ -37,10 +37,11 @@ Note:
 In order to enable compression backend's multi stream support max_comp_streams
 must be initially set to desired concurrency level before ZRAM device
 initialisation. Once the device initialised as a single stream compression
-backend (max_comp_streams equals to 0) changing the value of max_comp_streams
-will not take any effect, because single stream compression backend implemented
-as a special case and does not support dynamic max_comp_streams. Only multi
-stream backend supports dynamic max_comp_streams adjustment.
+backend (max_comp_streams equals to 1), you will see error if you try to change
+the value of max_comp_streams because single stream compression backend
+implemented as a special case by lock overhead issue and does not support
+dynamic max_comp_streams. Only multi stream backend supports dynamic
+max_comp_streams adjustment.
 
 3) Select compression algorithm
 	Using comp_algorithm device attribute one can see available and

drivers/block/zram/zcomp.c +2 -2

index 92a83df40a27..15fe6a27781b 100644
@@ -152,7 +152,7 @@ static void zcomp_strm_multi_release(struct zcomp *comp, struct zcomp_strm *zstr
 }
 
 /* change max_strm limit */
-static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	struct zcomp_strm_multi *zs = comp->stream;
 	struct zcomp_strm *zstrm;

@@ -171,7 +171,7 @@ static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 		zs->avail_strm--;
 	}
 	spin_unlock(&zs->strm_lock);
-	return 0;
+	return true;
 }
 
 static void zcomp_strm_multi_destroy(struct zcomp *comp)

drivers/block/zram/zcomp.c static void zcomp_strm_single_release(struct zcomp *comp, · line 238

Quoted 10 lines

drivers/block/zram/zcomp.c +2 -2

@@ -231,10 +231,10 @@ static void zcomp_strm_single_release(struct zcomp *comp,
 	mutex_unlock(&zs->strm_lock);
 }
 
-static int zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	/* zcomp_strm_single support only max_comp_streams == 1 */
-	return -ENOTSUPP;
+	return 0;
 }

IMHO, -ENOTSUPP for unsupported operation fits better than `false'. yes, currently there are only two possible returns:
0 -- success
-ENOTSUPP - not supported operation

Quoted 2 lines

though, we can extend functions later and return additional codes, other than false' and true'.

Thing to expose to user isn't true and false but EINVAL.

Quoted 3 lines

for example, -E2BIG if user requested extremly large number of streams, like 5000 streams.

I'm not sure it's right example for E2BIG.
When I read the comment, it says "argument list too long". Anyway, when I tried ENOTSUPP, echo doesn't show meaningful error to user and I dont' know it's casual err number for userspace.
Pz, comment about that.

Quoted 50 lines

drivers/block/zram/zcomp.c +1 -1

 static void zcomp_strm_single_destroy(struct zcomp *comp)

@@ -283,7 +283,7 @@ ssize_t zcomp_available_show(const char *comp, char *buf)
 	return sz;
 }
 
-int zcomp_set_max_streams(struct zcomp *comp, int num_strm)
+bool zcomp_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	return comp->set_max_streams(comp, num_strm);
 }

drivers/block/zram/zcomp.h +2 -2

index 8b8997f8613b..c59d1fca72c0 100644
@@ -46,7 +46,7 @@ struct zcomp {
 
 	struct zcomp_strm *(*strm_find)(struct zcomp *comp);
 	void (*strm_release)(struct zcomp *comp, struct zcomp_strm *zstrm);
-	int (*set_max_streams)(struct zcomp *comp, int num_strm);
+	bool (*set_max_streams)(struct zcomp *comp, int num_strm);
 	void (*destroy)(struct zcomp *comp);
 };

@@ -64,5 +64,5 @@ int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
 int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
 		size_t src_len, unsigned char *dst);
 
-int zcomp_set_max_streams(struct zcomp *comp, int num_strm);
+bool zcomp_set_max_streams(struct zcomp *comp, int num_strm);
 #endif /* _ZCOMP_H_ */

drivers/block/zram/zram_drv.c +4 -3

index 7631ef0cbc41..eead9db9b100 100644
@@ -128,17 +128,24 @@ static ssize_t max_comp_streams_store(struct device *dev,
 	struct zram *zram = dev_to_zram(dev);
 
 	if (kstrtoint(buf, 0, &num))
-		return -EINVAL;
+		goto out;
 	if (num < 1)
-		return -EINVAL;
+		goto out;
+
 	down_write(&zram->init_lock);
 	if (init_done(zram)) {
-		if (zcomp_set_max_streams(zram->comp, num))
+		if (!zcomp_set_max_streams(zram->comp, num)) {

Quoted 8 lines

drivers/block/zram/zram_drv.c static ssize_t max_comp_streams_store(struct device *dev, · line 143
Quoted 6 lines
drivers/block/zram/zram_drv.c +3 -0
 			pr_info("Cannot change max compression streams\n");
+			goto out_unlock;
+		}
 	}
+
 	zram->max_comp_streams = num;
agree, better to avoid this for a single stream.

Yeb.

Signature · 2 lines

Kind regards,
Minchan Kim

Sergey Senozhatsky

2014-03-09 17:02 UTC #3 lore raw

Hello Minchan,

Quoted 79 lines · Minchan Kim

Hello Sergey!

Quoted 76 lines · Sergey Senozhatsky

Quoted 59 lines · Minchan Kim

This patch prevents max_comp_streams's change when zcomp was initialized as single zcomp and emit the error to user(ex, echo).

Signed-off-by Minchan Kim <[email protected]>

---
 Documentation/blockdev/zram.txt |  9 +++++----
 drivers/block/zram/zcomp.c      | 10 +++++-----
 drivers/block/zram/zcomp.h      |  4 ++--
 drivers/block/zram/zram_drv.c   | 15 +++++++++++----
 4 files changed, 23 insertions(+), 15 deletions(-)

Documentation/blockdev/zram.txt +5 -4

index 2604ffed51db..0595c3f56ccf 100644
@@ -37,10 +37,11 @@ Note:
 In order to enable compression backend's multi stream support max_comp_streams
 must be initially set to desired concurrency level before ZRAM device
 initialisation. Once the device initialised as a single stream compression
-backend (max_comp_streams equals to 0) changing the value of max_comp_streams
-will not take any effect, because single stream compression backend implemented
-as a special case and does not support dynamic max_comp_streams. Only multi
-stream backend supports dynamic max_comp_streams adjustment.
+backend (max_comp_streams equals to 1), you will see error if you try to change
+the value of max_comp_streams because single stream compression backend
+implemented as a special case by lock overhead issue and does not support
+dynamic max_comp_streams. Only multi stream backend supports dynamic
+max_comp_streams adjustment.
 
 3) Select compression algorithm
 	Using comp_algorithm device attribute one can see available and

drivers/block/zram/zcomp.c +2 -2

index 92a83df40a27..15fe6a27781b 100644
@@ -152,7 +152,7 @@ static void zcomp_strm_multi_release(struct zcomp *comp, struct zcomp_strm *zstr
 }
 
 /* change max_strm limit */
-static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	struct zcomp_strm_multi *zs = comp->stream;
 	struct zcomp_strm *zstrm;

@@ -171,7 +171,7 @@ static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 		zs->avail_strm--;
 	}
 	spin_unlock(&zs->strm_lock);
-	return 0;
+	return true;
 }
 
 static void zcomp_strm_multi_destroy(struct zcomp *comp)

drivers/block/zram/zcomp.c static void zcomp_strm_single_release(struct zcomp *comp, · line 238

Quoted 10 lines

drivers/block/zram/zcomp.c +2 -2

@@ -231,10 +231,10 @@ static void zcomp_strm_single_release(struct zcomp *comp,
 	mutex_unlock(&zs->strm_lock);
 }
 
-static int zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	/* zcomp_strm_single support only max_comp_streams == 1 */
-	return -ENOTSUPP;
+	return 0;
 }

IMHO, -ENOTSUPP for unsupported operation fits better than `false'. yes, currently there are only two possible returns:
0 -- success
-ENOTSUPP - not supported operation

Quoted 5 lines

Quoted 2 lines
though, we can extend functions later and return additional codes, other than false' and true'.
Thing to expose to user isn't true and false but EINVAL.

sure. I mean we can return actual zcomp_set_max_streams() error (if any) back to user from max_comp_streams_store():

	[..]
	ret = zcomp_set_max_streams(...);
	[..]
	return ret;

Quoted 10 lines

Quoted 3 lines
for example, -E2BIG if user requested extremly large number of streams, like 5000 streams.
I'm not sure it's right example for E2BIG.
When I read the comment, it says "argument list too long". Anyway, when I tried ENOTSUPP, echo doesn't show meaningful error to user and I dont' know it's casual err number for userspace.
Pz, comment about that.

E2BIG (introduced by POSIX.1-2001) was a quick example and, probably, not the perfect one. In general, I'm not against this change and I can live with zcomp_set_max_streams() returning bool.

-ss

Quoted 65 lines

Quoted 50 lines

drivers/block/zram/zcomp.c +1 -1

 static void zcomp_strm_single_destroy(struct zcomp *comp)

@@ -283,7 +283,7 @@ ssize_t zcomp_available_show(const char *comp, char *buf)
 	return sz;
 }
 
-int zcomp_set_max_streams(struct zcomp *comp, int num_strm)
+bool zcomp_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	return comp->set_max_streams(comp, num_strm);
 }

drivers/block/zram/zcomp.h +2 -2

index 8b8997f8613b..c59d1fca72c0 100644
@@ -46,7 +46,7 @@ struct zcomp {
 
 	struct zcomp_strm *(*strm_find)(struct zcomp *comp);
 	void (*strm_release)(struct zcomp *comp, struct zcomp_strm *zstrm);
-	int (*set_max_streams)(struct zcomp *comp, int num_strm);
+	bool (*set_max_streams)(struct zcomp *comp, int num_strm);
 	void (*destroy)(struct zcomp *comp);
 };

@@ -64,5 +64,5 @@ int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
 int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
 		size_t src_len, unsigned char *dst);
 
-int zcomp_set_max_streams(struct zcomp *comp, int num_strm);
+bool zcomp_set_max_streams(struct zcomp *comp, int num_strm);
 #endif /* _ZCOMP_H_ */

drivers/block/zram/zram_drv.c +4 -3

index 7631ef0cbc41..eead9db9b100 100644
@@ -128,17 +128,24 @@ static ssize_t max_comp_streams_store(struct device *dev,
 	struct zram *zram = dev_to_zram(dev);
 
 	if (kstrtoint(buf, 0, &num))
-		return -EINVAL;
+		goto out;
 	if (num < 1)
-		return -EINVAL;
+		goto out;
+
 	down_write(&zram->init_lock);
 	if (init_done(zram)) {
-		if (zcomp_set_max_streams(zram->comp, num))
+		if (!zcomp_set_max_streams(zram->comp, num)) {

Quoted 8 lines

drivers/block/zram/zram_drv.c static ssize_t max_comp_streams_store(struct device *dev, · line 143
Quoted 6 lines
drivers/block/zram/zram_drv.c +3 -0
 			pr_info("Cannot change max compression streams\n");
+			goto out_unlock;
+		}
 	}
+
 	zram->max_comp_streams = num;
agree, better to avoid this for a single stream.

Yeb.

Signature · 2 lines

Kind regards,
Minchan Kim

Minchan Kim

author maintainer

2014-03-10 02:01 UTC #4 lore raw

Hello Sergey,

Quoted 107 lines · Sergey Senozhatsky

Hello Minchan,
Quoted 79 lines · Minchan Kim
Hello Sergey!
Quoted 76 lines · Sergey Senozhatsky
Quoted 59 lines · Minchan Kim
When we initialized zcomp with single, we couldn't change max_comp_streams without zram reset but current interface doesn't show any error to user and even it changes max_comp_streams's value without any effect so it would make user very confusing.
This patch prevents max_comp_streams's change when zcomp was initialized as single zcomp and emit the error to user(ex, echo).
Signed-off-by Minchan Kim <[email protected]>
---
 Documentation/blockdev/zram.txt |  9 +++++----
 drivers/block/zram/zcomp.c      | 10 +++++-----
 drivers/block/zram/zcomp.h      |  4 ++--
 drivers/block/zram/zram_drv.c   | 15 +++++++++++----
 4 files changed, 23 insertions(+), 15 deletions(-)
Documentation/blockdev/zram.txt +5 -4
index 2604ffed51db..0595c3f56ccf 100644
@@ -37,10 +37,11 @@ Note:
 In order to enable compression backend's multi stream support max_comp_streams
 must be initially set to desired concurrency level before ZRAM device
 initialisation. Once the device initialised as a single stream compression
-backend (max_comp_streams equals to 0) changing the value of max_comp_streams
-will not take any effect, because single stream compression backend implemented
-as a special case and does not support dynamic max_comp_streams. Only multi
-stream backend supports dynamic max_comp_streams adjustment.
+backend (max_comp_streams equals to 1), you will see error if you try to change
+the value of max_comp_streams because single stream compression backend
+implemented as a special case by lock overhead issue and does not support
+dynamic max_comp_streams. Only multi stream backend supports dynamic
+max_comp_streams adjustment.
 
 3) Select compression algorithm
 	Using comp_algorithm device attribute one can see available and
drivers/block/zram/zcomp.c +2 -2
index 92a83df40a27..15fe6a27781b 100644
@@ -152,7 +152,7 @@ static void zcomp_strm_multi_release(struct zcomp *comp, struct zcomp_strm *zstr
 }
 
 /* change max_strm limit */
-static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	struct zcomp_strm_multi *zs = comp->stream;
 	struct zcomp_strm *zstrm;
@@ -171,7 +171,7 @@ static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 		zs->avail_strm--;
 	}
 	spin_unlock(&zs->strm_lock);
-	return 0;
+	return true;
 }
 
 static void zcomp_strm_multi_destroy(struct zcomp *comp)
drivers/block/zram/zcomp.c static void zcomp_strm_single_release(struct zcomp *comp, · line 238
Quoted 10 lines
drivers/block/zram/zcomp.c +2 -2
@@ -231,10 +231,10 @@ static void zcomp_strm_single_release(struct zcomp *comp,
 	mutex_unlock(&zs->strm_lock);
 }
 
-static int zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	/* zcomp_strm_single support only max_comp_streams == 1 */
-	return -ENOTSUPP;
+	return 0;
 }
IMHO, -ENOTSUPP for unsupported operation fits better than `false'. yes, currently there are only two possible returns:
0 -- success
-ENOTSUPP - not supported operation
Quoted 5 lines
Quoted 2 lines
though, we can extend functions later and return additional codes, other than false' and true'.
Thing to expose to user isn't true and false but EINVAL.
sure. I mean we can return actual zcomp_set_max_streams() error (if any) back to user from max_comp_streams_store():
	[..]
	ret = zcomp_set_max_streams(...);
	[..]
	return ret;
Quoted 10 lines
Quoted 3 lines
for example, -E2BIG if user requested extremly large number of streams, like 5000 streams.
I'm not sure it's right example for E2BIG.
When I read the comment, it says "argument list too long". Anyway, when I tried ENOTSUPP, echo doesn't show meaningful error to user and I dont' know it's casual err number for userspace.
Pz, comment about that.

Quoted 3 lines

E2BIG (introduced by POSIX.1-2001) was a quick example and, probably, not the perfect one. In general, I'm not against this change and I can live with zcomp_set_max_streams() returning bool.

Then, could you give me Acked-by?
I am hungry with that. :)

Signature · 2 lines

Kind regards,
Minchan Kim

Sergey Senozhatsky

Acked-by

2014-03-10 07:54 UTC #5 lore raw

Hello,

Quoted 110 lines · Minchan Kim

Hello Sergey,
Quoted 107 lines · Sergey Senozhatsky
Hello Minchan,
Quoted 79 lines · Minchan Kim
Hello Sergey!
Quoted 76 lines · Sergey Senozhatsky
Quoted 59 lines · Minchan Kim
When we initialized zcomp with single, we couldn't change max_comp_streams without zram reset but current interface doesn't show any error to user and even it changes max_comp_streams's value without any effect so it would make user very confusing.
This patch prevents max_comp_streams's change when zcomp was initialized as single zcomp and emit the error to user(ex, echo).
Signed-off-by Minchan Kim <[email protected]>
---
 Documentation/blockdev/zram.txt |  9 +++++----
 drivers/block/zram/zcomp.c      | 10 +++++-----
 drivers/block/zram/zcomp.h      |  4 ++--
 drivers/block/zram/zram_drv.c   | 15 +++++++++++----
 4 files changed, 23 insertions(+), 15 deletions(-)
Documentation/blockdev/zram.txt +5 -4
index 2604ffed51db..0595c3f56ccf 100644
@@ -37,10 +37,11 @@ Note:
 In order to enable compression backend's multi stream support max_comp_streams
 must be initially set to desired concurrency level before ZRAM device
 initialisation. Once the device initialised as a single stream compression
-backend (max_comp_streams equals to 0) changing the value of max_comp_streams
-will not take any effect, because single stream compression backend implemented
-as a special case and does not support dynamic max_comp_streams. Only multi
-stream backend supports dynamic max_comp_streams adjustment.
+backend (max_comp_streams equals to 1), you will see error if you try to change
+the value of max_comp_streams because single stream compression backend
+implemented as a special case by lock overhead issue and does not support
+dynamic max_comp_streams. Only multi stream backend supports dynamic
+max_comp_streams adjustment.
 
 3) Select compression algorithm
 	Using comp_algorithm device attribute one can see available and
drivers/block/zram/zcomp.c +2 -2
index 92a83df40a27..15fe6a27781b 100644
@@ -152,7 +152,7 @@ static void zcomp_strm_multi_release(struct zcomp *comp, struct zcomp_strm *zstr
 }
 
 /* change max_strm limit */
-static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	struct zcomp_strm_multi *zs = comp->stream;
 	struct zcomp_strm *zstrm;
@@ -171,7 +171,7 @@ static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
 		zs->avail_strm--;
 	}
 	spin_unlock(&zs->strm_lock);
-	return 0;
+	return true;
 }
 
 static void zcomp_strm_multi_destroy(struct zcomp *comp)
drivers/block/zram/zcomp.c static void zcomp_strm_single_release(struct zcomp *comp, · line 238
Quoted 10 lines
drivers/block/zram/zcomp.c +2 -2
@@ -231,10 +231,10 @@ static void zcomp_strm_single_release(struct zcomp *comp,
 	mutex_unlock(&zs->strm_lock);
 }
 
-static int zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
+static bool zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
 {
 	/* zcomp_strm_single support only max_comp_streams == 1 */
-	return -ENOTSUPP;
+	return 0;
 }
IMHO, -ENOTSUPP for unsupported operation fits better than `false'. yes, currently there are only two possible returns:
0 -- success
-ENOTSUPP - not supported operation
Quoted 5 lines
Quoted 2 lines
though, we can extend functions later and return additional codes, other than false' and true'.
Thing to expose to user isn't true and false but EINVAL.
sure. I mean we can return actual zcomp_set_max_streams() error (if any) back to user from max_comp_streams_store():
	[..]
	ret = zcomp_set_max_streams(...);
	[..]
	return ret;
Quoted 10 lines
Quoted 3 lines
for example, -E2BIG if user requested extremly large number of streams, like 5000 streams.
I'm not sure it's right example for E2BIG.
When I read the comment, it says "argument list too long". Anyway, when I tried ENOTSUPP, echo doesn't show meaningful error to user and I dont' know it's casual err number for userspace.
Pz, comment about that.

Quoted 7 lines

Quoted 3 lines
E2BIG (introduced by POSIX.1-2001) was a quick example and, probably, not the perfect one. In general, I'm not against this change and I can live with zcomp_set_max_streams() returning bool.
Then, could you give me Acked-by?
I am hungry with that. :)

sure :)

Acked-by Sergey Senozhatsky <[email protected]>

-ss

Quoted 4 lines

Signature · 2 lines
Kind regards,
Minchan Kim