Re: zram OOM behavior

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On Fri, Sep 28, 2012 at 1:32 PM, Luigi Semenzato <semenzato@xxxxxxxxxx> wrote:
> Greetings,
>
> We are experimenting with zram in Chrome OS.  It works quite well
> until the system runs out of memory, at which point it seems to hang,
> but we suspect it is thrashing.

Or spinning in some sad loop. Does the kernel have the CONFIG_DETECT_*
options to figure out what is happening? Can you invoke the Alt-SysRQ
when it is hung?
>
> Before the (apparent) hang, the OOM killer gets rid of a few
> processes, but then the other processes gradually stop responding,
> until the entire system becomes unresponsive.

Does the OOM give you an idea what the memory state is? Can you
actually provide the dmesg?

>
> I am wondering if anybody has run into this.  Thanks!
>
> Luigi
>
> P.S.  For those who wish to know more:
>
> 1. We use the min_filelist_kbytes patch
> (http://lwn.net/Articles/412313/)  (I am not sure if it made it into
> the standard kernel) and set min_filelist_kbytes to 50Mb.  (This may
> not matter, as it's unlikely to make things worse.)
>
> 2. We swap only to compressed ram.  The setup is very simple:
>
>  echo ${ZRAM_SIZE_KB}000 >/sys/block/zram0/disksize ||
>       logger -t "$UPSTART_JOB" "failed to set zram size"
>   mkswap /dev/zram0 || logger -t "$UPSTART_JOB" "mkswap /dev/zram0 failed"
>   swapon /dev/zram0 || logger -t "$UPSTART_JOB" "swapon /dev/zram0 failed"
>
> For ZRAM_SIZE_KB, we typically use 1.5 the size of RAM (which is 2 or
> 4 Gb).  The compression factor is about 3:1.  The hangs happen for
> quite a wide range of zram sizes.
>
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