• Minchan Kim's avatar
    zram: promote zram from staging · cd67e10a
    Minchan Kim authored
    Zram has lived in staging for a LONG LONG time and have been
    fixed/improved by many contributors so code is clean and stable now.  Of
    course, there are lots of product using zram in real practice.
    
    The major TV companys have used zram as swap since two years ago and
    recently our production team released android smart phone with zram
    which is used as swap, too and recently Android Kitkat start to use zram
    for small memory smart phone.  And there was a report Google released
    their ChromeOS with zram, too and cyanogenmod have been used zram long
    time ago.  And I heard some disto have used zram block device for tmpfs.
    In addition, I saw many report from many other peoples.  For example,
    Lubuntu start to use it.
    
    The benefit of zram is very clear.  With my experience, one of the
    benefit was to remove jitter of video application with backgroud memory
    pressure.  It would be effect of efficient memory usage by compression
    but more issue is whether swap is there or not in the system.  Recent
    mobile platforms have used JAVA so there are many anonymous pages.  But
    embedded system normally are reluctant to use eMMC or SDCard as swap
    because there is wear-leveling and latency issues so if we do not use
    swap, it means we can't reclaim anoymous pages and at last, we could
    encounter OOM kill.  :(
    
    Although we have real storage as swap, it was a problem, too.  Because
    it sometime ends up making system very unresponsible caused by slow swap
    storage performance.
    
    Quote from Luigi on Google
     "Since Chrome OS was mentioned: the main reason why we don't use swap
      to a disk (rotating or SSD) is because it doesn't degrade gracefully
      and leads to a bad interactive experience.  Generally we prefer to
      manage RAM at a higher level, by transparently killing and restarting
      processes.  But we noticed that zram is fast enough to be competitive
      with the latter, and it lets us make more efficient use of the
      available RAM.  " and he announced.
    http://www.spinics.net/lists/linux-mm/msg57717.html
    
    Other uses case is to use zram for block device.  Zram is block device
    so anyone can format the block device and mount on it so some guys on
    the internet start zram as /var/tmp.
    http://forums.gentoo.org/viewtopic-t-838198-start-0.html
    
    Let's promote zram and enhance/maintain it instead of removing.
    Signed-off-by: default avatarMinchan Kim <minchan@kernel.org>
    Reviewed-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Acked-by: default avatarNitin Gupta <ngupta@vflare.org>
    Acked-by: default avatarPekka Enberg <penberg@kernel.org>
    Cc: Bob Liu <bob.liu@oracle.com>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Jens Axboe <axboe@kernel.dk>
    Cc: Luigi Semenzato <semenzato@google.com>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    cd67e10a
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