Re: mmap vs fs cache

Howard Chu
2013-03-11T12:40:51Z

Jan Kara wrote:
> On Fri 08-03-13 12:04:46, Howard Chu wrote:
>> The test clearly is accessing only 30GB of data. Once slapd reaches
>> this process size, the test can be stopped and restarted any number
>> of times, run for any number of hours continuously, and memory use
>> on the system is unchanged, and no pageins occur.
> Interesting. It might be worth trying what happens if you do
> madvise(..., MADV_DONTNEED) on the data file instead of dropping caches
> with /proc/sys/vm/drop_caches. That way we can establish whether the extra
> cached data is in the data file (things will look the same way as with
> drop_caches) or somewhere else (there will be still unmapped page cache).

I screwed up. My madvise(RANDOM) call used the wrong address/len so it didn't
cover the whole region. After fixing this, the test now runs as expected - the
slapd process size grows to 30GB without any problem. Sorry for the noise.

--
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/