On Thu, 7 Jan 2016 16:34:36 +0000
Robert Kierski <rkierski@xxxxxxxx> wrote:
> As far as adjusting stripe_cache_size... The stripe cache is dynamically allocated. It won't save any RAM by decreasing stripe_cache_size.
Since when?
# echo 512 > /sys/devices/virtual/block/md0/md/stripe_cache_size
# free
total used free shared buffers cached
Mem: 16159912 15672696 487216 12588 52 14484708
-/+ buffers/cache: 1187936 14971976
Swap: 0 0 0
# echo 32768 > /sys/devices/virtual/block/md0/md/stripe_cache_size
# free
total used free shared buffers cached
Mem: 16159912 15957880 202032 12588 52 14214952
-/+ buffers/cache: 1742876 14417036
Swap: 0 0 0
You can see that's not the case (on kernel 4.3.3 with four-member RAID5);
And it's quite easy to rapidly hit OOM issues on high-member-count arrays by
setting stripe_cache_size to larger values (not realizing that this is *in
pages* not kilobytes or sectors, and *per disk*).
As for the original question, try checking stripe_cache_active e.g. once
per second during heavy write load to the filesystem.
--
With respect,
Roman
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