Another performance related problem I am seeing due to nilfs_cleanerd
is that it causes unhealthy amounts of cache churn. It's reads and
writes are buffered, which inevitably means that things it reads will
get cached. Since it is going through all the blocks on the fs that have
any garbage to collect, it will eat through all the available memory
pretty quickly. It also means that it will push out of caches things
that really should stay in caches.
Since cleanerd's actual disk I/O is going to have no correlation with
actual file access pattern, is there a way to make cleanerd always
operate with something like the O_DIRECT flag so that is's reads won't
fill up the page cache?
This is a pretty serious problem on small machines running of cheap
flash (think ARM machines with 512MB of RAM and slow flash media).
The quick and dirty workaround I am pondering at the moment is to set
up a cron job that runs once/minute, checks df, and starts/kills
nilfs_cleanerd depending on how much free space is available, but that's
not really a solution.
Gordan
--
To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
