not ramp up to max size anyway. What I want is to bump up max size, so that when kernel detects sequential worklaod
it does not restrict itself to 32 pages.
I looked around and saw an old patch that tried to account for actual memory on the system and setting max_readahead
according to that. Restricting to arbitrary limits -- for instance think 512MB system vs 4GB system - is not sane IMO.
Shailesh Jain
On Fri, Sep 25, 2009 at 6:00 PM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote:
not sure why u want to change that? for a specific performanceOn 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
>
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
