From: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Subject: 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@xxxxxxxxx Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/blockdev/zram.txt | 25 ++++------------ drivers/block/zram/zcomp.c | 5 --- drivers/block/zram/zram_drv.c | 45 +++++++----------------------- drivers/block/zram/zram_drv.h | 1 4 files changed, 18 insertions(+), 58 deletions(-) diff -puN Documentation/blockdev/zram.txt~zram-remove-max_comp_streams-internals Documentation/blockdev/zram.txt --- a/Documentation/blockdev/zram.txt~zram-remove-max_comp_streams-internals +++ a/Documentation/blockdev/zram.txt @@ -59,27 +59,16 @@ num_devices parameter is optional and te 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. + 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. - Examples: - #show max compression streams number + 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, diff -puN drivers/block/zram/zcomp.c~zram-remove-max_comp_streams-internals drivers/block/zram/zcomp.c --- a/drivers/block/zram/zcomp.c~zram-remove-max_comp_streams-internals +++ a/drivers/block/zram/zcomp.c @@ -95,11 +95,6 @@ bool zcomp_available_algorithm(const cha 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); diff -puN drivers/block/zram/zram_drv.c~zram-remove-max_comp_streams-internals drivers/block/zram/zram_drv.c --- a/drivers/block/zram/zram_drv.c~zram-remove-max_comp_streams-internals +++ a/drivers/block/zram/zram_drv.c @@ -304,46 +304,25 @@ static ssize_t mem_used_max_store(struct 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 zra /* 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; diff -puN drivers/block/zram/zram_drv.h~zram-remove-max_comp_streams-internals drivers/block/zram/zram_drv.h --- a/drivers/block/zram/zram_drv.h~zram-remove-max_comp_streams-internals +++ a/drivers/block/zram/zram_drv.h @@ -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 */ _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
