On Fri, Sep 25, 2009 at 12:05 AM, shailesh jain <coolworldofshail@xxxxxxxxx> wrote: > Hi, > Is the maximum limit of readahead 128KB ? .. Can it be changed by FS > kernel module ? > > > Shailesh Jain > not sure why u want to change that? for a specific performance tuning scenario (lots of sequential read)? this readahead feature is useful only if u are intending on reading large files. But if u switch to a different files, assuming many small files, u defeats the purpose of readahead. i think this is an OS-independent features, which is specifically tuned to the normal usage of the filesystem. so, for example for AIX: http://publib.boulder.ibm.com/infocenter/systems/index.jsp?topic=/com.ibm.aix.prftungd/doc/prftungd/seq_read_perf_tuning.htm their readahead is only (max) 16xpagesize. not sure how big is that, but our 128KB should be > 16xpagesize (how big is our IO blocksize anyway?) for another reputable references: http://www.dba-oracle.com/t_read_ahead_cache_windows.htm (in Oracle database). The problem is that if u read ahead too much, and after that the entire buffer is going to be thrown away due to un-use, then a lot of time is wasted in reading ahead. -- Regards, Peter Teoh -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
