slab_reassign_evictions_nomem

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theonajim

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Aug 27, 2020, 1:51:03 PM8/27/20
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We are using version 1.6.6 of memcached with extstore enabled and we are observing records being evicted but evictions stat reports 0. slab_reassign_evictions_nomem stat does show items being evicted. How do we avoid losing records due to slab_reassign_evictions_nomem ? Also, is there a reason it is not counted as a regular eviction?
 'stats' 'stats settings' 'stats items' 'stats slabs' output are attached.

Thanks,
--Theo

output.txt

dormando

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Sep 16, 2020, 12:00:42 AM9/16/20
to 'theonajim' via memcached
Hey,

Sorry for the super late reply.

I'm tracking a fix for this here:
https://github.com/memcached/memcached/issues/541 - but not entirely sure
when I'll get to it. It's not easy to avoid but should be relatively rare.
It happens when the system thinks it has enough memory free to move a
page, but by the time it does the memory's been assigned elsewhere.
Restructuring would fix it.

If it's a huge problem, you can either disable/pause the page mover or
change the minimum pages it reserves from a source slab class... which I
think might be hard coded :(

The stat not counting in general evictions is another long standing issue.
(apparently reported in 2017?)

I'll see if I can do the restructuring sooner than later. We really
shouldn't lose items at random when moving pages, they should at least be
pulled from the LRU tail.
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