Re: OOM killer changes

[Michal Hocko <mhocko@suse.cz>]

On Mon 01-08-16 12:52:40, Ralf-Peter Rohbeck wrote:
> On 01.08.2016 12:43, Michal Hocko wrote:
> > On Mon 01-08-16 12:35:51, Ralf-Peter Rohbeck wrote:
> > > On 01.08.2016 12:26, Michal Hocko wrote:
> > [...]
> > > > the amount of dirty pages is much smaller as well as the anonymous
> > > > memory. The biggest portion seems to be in the page cache. The memory
> > > The page cache will always be full if I'm writing at full steam to multiple
> > > drives, no?
> > Yes, the memory full of page cache is not unusual. The large portion of
> > that memory being dirty/writeback can be a problem. That is why we have
> > a dirty memory throttling which slows down (throttles) writers to keep
> > the amount reasonable. What is your dirty throttling setup?
> > $ grep . /proc/sys/vm/dirty*
> > 
> > and what is your storage setup?
> 
> root@fs:~# grep . /proc/sys/vm/dirty*
> /proc/sys/vm/dirty_background_bytes:0
> /proc/sys/vm/dirty_background_ratio:10
> /proc/sys/vm/dirty_bytes:0
> /proc/sys/vm/dirty_expire_centisecs:3000
> /proc/sys/vm/dirty_ratio:20

With your 8G of RAM this can be quite a lot of dirty data at once. Is
your storage able to write that back in a reasonable time? I mean this
shouldn't cause the OOM killer but it can lead to some unexpected stalls
especially when there are a lot of writers AFAIU. dirty_bytes knob
should help to define a better cap.

> /proc/sys/vm/dirtytime_expire_seconds:43200
> /proc/sys/vm/dirty_writeback_centisecs:500
> 
> 
> Storage setup:
> 
> root@fs:~# lsscsi
> [0:2:0:0]    disk    LSI      MR9271-8iCC      3.29  /dev/sda
> [0:2:1:0]    disk    LSI      MR9271-8iCC      3.29  /dev/sdb
> [9:0:0:0]    disk    TOSHIBA  External USB 3.0 5438  /dev/sdf
> [10:0:0:0]   disk    Seagate  Backup+ Desk     050B  /dev/sdc
> [11:0:0:0]   disk    Seagate  Expansion Desk   9400  /dev/sdd
> [12:0:0:0]   disk    Seagate  Backup+ Desk     050B /dev/sde
> [13:0:0:0]   disk    Seagate  Expansion Desk   9400 /dev/sdg
> [14:0:0:0]   disk    TOSHIBA  External USB 3.0 5438 /dev/sdl
> [15:0:0:0]   disk    Seagate  Expansion Desk   9400 /dev/sdh
> [16:0:0:0]   disk    Seagate  Expansion Desk   9400 /dev/sdi
> [17:0:0:0]   disk    TOSHIBA  External USB 3.0 5438 /dev/sdm
> [18:0:0:0]   disk    Seagate  Expansion Desk   9400 /dev/sdj
> [19:0:0:0]   disk    Seagate  Expansion Desk   9400  /dev/sdk
> 
> sda is a 6x 1TB RAID5 and sdb is a single 480GB SSD, both on a MegaRAID
> controller.
> 
> The rest are 4TB USB drives that I'm experimenting with.

Which devices did you write when hitting the OOM killer?
-- 
Michal Hocko
SUSE Labs

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