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>

3 files changed, 11 insertions, 40 deletions

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index bc98d5ed5477..b51a816d766b 100644
--- 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 f92965c4229b..8fcfbebe79cd 100644
--- 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 8e92339686d7..06b1636f4722 100644
--- 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 */