From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gordan Bobic Subject: Cache Churn Date: Wed, 10 Aug 2011 12:17:45 +0100 Message-ID: <09449c6acbe526ffa056cf4b7d005032@mail.shatteredsilicon.net> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: Sender: linux-nilfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: linux-nilfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org 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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html