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Commit 43209ea2 authored by Sergey Senozhatsky's avatar Sergey Senozhatsky Committed by Linus Torvalds
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zram: remove max_comp_streams internals 

Remove the internal part of max_comp_streams interface, since we
switched to per-cpu streams.  We will keep RW max_comp_streams attr
around, because:

a) we may (silently) switch back to idle compression streams list and
   don't want to disturb user space

b) max_comp_streams attr must wait for the next 'lay off cycle'; we
   give user space 2 years to adjust before we remove/downgrade the attr,
   and there are already several attrs scheduled for removal in 4.11, so
   it's too late for max_comp_streams.

This slightly change a user visible behaviour:

- First, reading from max_comp_stream file now will always return the
  number of online CPUs.

- Second, writing to max_comp_stream will not take any effect.

Link: http://lkml.kernel.org/r/20160503165546.25201-1-sergey.senozhatsky@gmail.com


Signed-off-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d34f6157

Documentation/blockdev/zram.txt

+8 −19
Original line number Diff line number Diff line
@@ -59,27 +59,16 @@ num_devices parameter is optional and tells zram how many devices should be 
pre-created. Default: 1.



2) Set max number of compression streams

	Compression backend may use up to max_comp_streams compression streams,

	thus allowing up to max_comp_streams concurrent compression operations.

	By default, compression backend uses single compression stream.



	Examples:

	#show max compression streams number

	Regardless the value passed to this attribute, ZRAM will always

	allocate multiple compression streams - one per online CPUs - thus

	allowing several concurrent compression operations. The number of

	allocated compression streams goes down when some of the CPUs

	become offline. There is no single-compression-stream mode anymore,

	unless you are running a UP system or has only 1 CPU online.



	To find out how many streams are currently available:

	cat /sys/block/zram0/max_comp_streams



	#set max compression streams number to 3

	echo 3 > /sys/block/zram0/max_comp_streams



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 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

	currently selected (shown in square brackets) compression algorithms,

drivers/block/zram/zcomp.c

+0 −5
Original line number Diff line number Diff line
@@ -95,11 +95,6 @@ bool zcomp_available_algorithm(const char *comp) 
	return find_backend(comp) != NULL;

}



bool zcomp_set_max_streams(struct zcomp *comp, int num_strm)

{

	return true;

}



struct zcomp_strm *zcomp_strm_find(struct zcomp *comp)

{

	return *get_cpu_ptr(comp->stream);

drivers/block/zram/zram_drv.c

+11 −34
Original line number Diff line number Diff line
@@ -304,46 +304,25 @@ static ssize_t mem_used_max_store(struct device *dev, 
	return len;

}



/*

 * We switched to per-cpu streams and this attr is not needed anymore.

 * However, we will keep it around for some time, because:

 * a) we may revert per-cpu streams in the future

 * b) it's visible to user space and we need to follow our 2 years

 *    retirement rule; but we already have a number of 'soon to be

 *    altered' attrs, so max_comp_streams need to wait for the next

 *    layoff cycle.

 */

static ssize_t max_comp_streams_show(struct device *dev,

		struct device_attribute *attr, char *buf)

{

	int val;

	struct zram *zram = dev_to_zram(dev);



	down_read(&zram->init_lock);

	val = zram->max_comp_streams;

	up_read(&zram->init_lock);



	return scnprintf(buf, PAGE_SIZE, "%d\n", val);

	return scnprintf(buf, PAGE_SIZE, "%d\n", num_online_cpus());

}



static ssize_t max_comp_streams_store(struct device *dev,

		struct device_attribute *attr, const char *buf, size_t len)

{

	int num;

	struct zram *zram = dev_to_zram(dev);

	int ret;



	ret = kstrtoint(buf, 0, &num);

	if (ret < 0)

		return ret;

	if (num < 1)

		return -EINVAL;



	down_write(&zram->init_lock);

	if (init_done(zram)) {

		if (!zcomp_set_max_streams(zram->comp, num)) {

			pr_info("Cannot change max compression streams\n");

			ret = -EINVAL;

			goto out;

		}

	}



	zram->max_comp_streams = num;

	ret = len;

out:

	up_write(&zram->init_lock);

	return ret;

	return len;

}



static ssize_t comp_algorithm_show(struct device *dev,
@@ -1035,7 +1014,6 @@ static void zram_reset_device(struct zram *zram) 
	/* Reset stats */

	memset(&zram->stats, 0, sizeof(zram->stats));

	zram->disksize = 0;

	zram->max_comp_streams = 1;



	set_capacity(zram->disk, 0);

	part_stat_set_all(&zram->disk->part0, 0);
@@ -1299,7 +1277,6 @@ static int zram_add(void) 
	}

	strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));

	zram->meta = NULL;

	zram->max_comp_streams = 1;



	pr_info("Added device: %s\n", zram->disk->disk_name);

	return device_id;

drivers/block/zram/zram_drv.h

+0 −1
Original line number Diff line number Diff line
@@ -102,7 +102,6 @@ struct zram { 
	 * the number of pages zram can consume for storing compressed data

	 */

	unsigned long limit_pages;

	int max_comp_streams;



	struct zram_stats stats;

	atomic_t refcount; /* refcount for zram_meta */