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hash: drop bees_unreadahead

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Forcing the entire hash table into immediate writeback causes crippling
write latencies at shutdown.  Even discarding pages as they are read in
at startup can trigger a writeback latency spike if the pages are dirty
at read time.

Better to let the VM subsystem handle this on its own.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell 2021-10-31 19:48:39 -04:00
parent 13ec4b5165
commit ff3b5a7a1b
1 changed files with 3 additions and 0 deletions
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3
src/bees-hash.cc
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@ -206,8 +206,11 @@ BeesHashTable::writeback_loop()
} }
catch_all([&]() { catch_all([&]() {
// trigger writeback on our way out // trigger writeback on our way out
#if 0
// seems to trigger huge latency spikes
BEESTOOLONG("unreadahead hash table size " << pretty(m_size)); BEESTOOLONG("unreadahead hash table size " << pretty(m_size));
bees_unreadahead(m_fd, 0, m_size); bees_unreadahead(m_fd, 0, m_size);
#endif
}); });
BEESLOGDEBUG("Exited hash table writeback_loop"); BEESLOGDEBUG("Exited hash table writeback_loop");
} }