Cc Minchan Kim, Jerome Marchand, Nitin Gupta, linux-kernel On (08/05/14 23:36), Sami Kerola wrote: > On 4 August 2014 12:55, Karel Zak <kzak@xxxxxxxxxx> wrote: > > On Mon, Aug 04, 2014 at 12:08:10AM +0100, Sami Kerola wrote: > >> Earlier the --algorithm and --streams had to be combined with --size. To > >> user requirement to combine with --size was indirectly told using > >> following message. > > > > And is it really supported by kernel? I see in > > Documentation/blockdev/zram.txt: > > > > 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. > > > > I guess that when you set disksize the zram device is "locked" for > > setting changes. It means that modify already initialized (created) > > zram devices is impossible. You have to reset the device to "unlock" > > the device setting. > > After playing with zramctl I found out --algorithm must be set before > --size yes. historically, storing the `size' == full device initialisation. I believe, it used to be so since the beginning of zram. compression algorithm selection was just plugged in into the existing scheme of things. > The --streams can be set after --size, but not if device is in use. > When device is in use none of the settings are allowed. you can't change compression algorithm on initialised/being used device. obviously. if zram has X pages compressed with lz0 then zram is supposed to use lz0 for decompression. 'streams' options is a little bit tricky. we have two different implementations for a single and multi stream backends. and there are reasons for that, to keep it short. if you create device with a single stream backend -- you can't change it any more. if you create device with a multi stream backend -- you can change the number of streams (though, it doesn't make a lot of sense to set streams to 1 in that case). iow, you can downgrade from multi stream to a multi stream device with only 1 stream (which is not identical to a single stream), but you can't upgrade a single stream device to a multi stream device. > $ ./zramctl > NAME ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT > /dev/zram0 lzo 100K 4K 76B 4K 2 [SWAP] > /dev/zram2 lzo 44K 0B 0B 0B 1 > /dev/zram3 lzo 1M 40K 796B 40K 1 /mnt > $ ./zramctl zram1 > NAME ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT > zram1 lzo 0B 0B 0B 0B 1 > > $ ./zramctl --algorithm lz4 zram1 ; echo $? > 0 > $ ./zramctl --algorithm lz4 zram2 ; echo $? > zramctl: zram2: failed to set algorithm: Device or resource busy > 1 > $ ./zramctl --algorithm lz4 zram3 ; echo $? > zramctl: zram3: failed to set algorithm: Device or resource busy > 1 > > $ ./zramctl --stream 2 zram1 ; echo $? > 0 > $ ./zramctl --stream 2 zram2 ; echo $? > 0 > $ ./zramctl --stream 2 zram3 ; echo $? > zramctl: zram3: failed to set number of streams: Invalid argument > 1 > > Whether the case --streams 2 zram2 in above example is correct or a > bug is a question to kernel developers (Sergey is CC'd). Looking the > commit message > > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=fe8eb122c82b2049c460fc6df6e8583a2f935cff > > the device behavior might be bug. > where? -ss -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
