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authorSergey Senozhatsky <sergey.senozhatsky@gmail.com>2016-05-20 16:59:59 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-05-20 17:58:30 -0700
commit43209ea2d17aae1540d4e28274e36404f72702f2 (patch)
treebe21fbbabf6fabeb3e1dd4ca2c0684f238458c55 /Documentation/blockdev/zram.txt
parentd34f615720d17c49b6779f6fcd5cb7eb82231a38 (diff)
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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: 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>
Diffstat (limited to 'Documentation/blockdev/zram.txt')
-rw-r--r--Documentation/blockdev/zram.txt27
1 files changed, 8 insertions, 19 deletions
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 5bda5031c83d..d88f0c70cd7f 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,