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: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 5bda503..d88f0c7 100644 (file)
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -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,

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index bc98d5e..b51a816 100644 (file)
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -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);

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index f92965c..8fcfbeb 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -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;

diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 8e92339..06b1636 100644 (file)
--- a/drivers/block/zram/zram_drv.h
+++ b/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 */