The test started to fail sporadically on jenkins after
7a00dd6985 due to quiesce() timing out. It's not
clear though if this is a regression because before the series such timeouts
would not cause test failure if the future resulves eventually, timeout was
only logged.
I was not able to reproduce it on my setup nor on jenkins, so let's add more
debugging output and trigger a coredump next time the test fails.
Message-Id: <1487089576-27147-1-git-send-email-tgrabiec@scylladb.com>
This reverts commit d61002cc33.
Introduced a regression in row_cache_alloc_stress.
The problem is that reclaim_from_evictable() evicts way too much after
the refactor due to the stop condition not taking into account how
much data was evicted so far and only looking at occupancy of the
minimal segment. This may lead to eviction of the whole region.
Currently eviction is performed until occupancy of the whole region
drops below the 85% threshold. This may take a while if region had
high occupancy and is large. We could improve the situation by only
evicting until occupancy of the sparsest segment drops below the
threshold, as is done by this change.
I tested this using a c-s read workload in which the condition
triggers in the cache region, with 1G per shard:
lsa-timing - Reclamation cycle took 12.934 us.
lsa-timing - Reclamation cycle took 47.771 us.
lsa-timing - Reclamation cycle took 125.946 us.
lsa-timing - Reclamation cycle took 144356 us.
lsa-timing - Reclamation cycle took 655.765 us.
lsa-timing - Reclamation cycle took 693.418 us.
lsa-timing - Reclamation cycle took 509.869 us.
lsa-timing - Reclamation cycle took 1139.15 us.
The 144ms pause is when large eviction is necessary.
The change improves worst case latency. Reclamation time statistics
over 30 second period after cache fills up, in microseconds:
Before:
avg = 1524.283148
stdev = 11021.021118
min = 12.934000
max = 144356.000000
sum = 257603.852000
samples = 169
After:
avg = 1317.362414
stdev = 1913.542802
min = 263.935000
max = 19244.600000
sum = 175209.201000
samples = 133
Refs #1634.
Message-Id: <1484730859-11969-1-git-send-email-tgrabiec@scylladb.com>
Large allocations test, unsurprisingly, allocates a lot of memory. Do
not leak it so that any tests that are going to be run afterwards have
still some memory left.
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
Originally, large allocation test case attempted to allocate an object
as big as halft of the space used by the lsa. That failed when the test
was executed with lower amount of memory available mainly due to the
memory fragmentation caused by previous test cases.
This patches reduces the size of the large allocation to 3/8 of the
total space used by the lsa which is still a lot but seems to make the
test pass even with as little memory as 64MB per shard.
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
Originally, lsa allocated each segment independently what could result
in high memory fragmentation. As a result many compaction and eviction
passes may be needed to release a sufficiently big contiguous memory
block.
These problems are solved by introduction of segment zones, contiguous
groups of segments. All segments are allocated from zones and the
algorithm tries to keep the number of zones to a minimum. Moreover,
segments can be migrated between zones or inside a zone in order to deal
with fragmentation inside zone.
Segment zones can be shrunk but cannot grow. Segment pool keeps a tree
containing all zones ordered by their base addresses. This tree is used
only by the memory reclamer. There is also a list of zones that have
at least one free segments that is used during allocation.
Segment allocation doesn't have any preferences which segment (and zone)
to choose. Each zone contains a free list of unused segments. If there
are no zones with free segments a new one is created.
Segment reclamation migrates segments from the zones higher in memory
to the ones at lower addresses. The remaining zones are shrunk until the
requested number of segments is reclaimed.
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
Disabling compaction of a region is currently done in order to keep
the references valid. But disabling only compaction is not enough, we
also need to disable eviction, as it also invalidates
references. Rather than introducing another type of lock, compaction
and eviction are controlled together, generalized as "reclaiming"
(hence the reclaim_lock).
It relies on the fact that the process has a fixed amount of memory
assigned and std::bad_alloc is thrown in a timely manner when it fills
up, which is the case for seastar's allocator, but not with the
default allocator. With the latter the OOM killer kills the process.
