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Date: Wed, 4 May 2016 01:55:46 +0900
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: [PATCH] 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.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
Documentation/blockdev/zram.txt | 27 ++++++++-----------------
drivers/block/zram/zcomp.c | 5 -----
drivers/block/zram/zram_drv.c | 45 ++++++++++-------------------------------
drivers/block/zram/zram_drv.h | 1 -
4 files changed, 19 insertions(+), 59 deletions(-)
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 5bda503..d88f0c7 100644
--- 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
--- 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
--- 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
--- 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 */
--
2.8.2.294.gbbc6168
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