Ralf Ertzinger wrote:
Hi.
On Fri, 28 Nov 2008 13:16:36 +0100, Phil Knirsch wrote:
Sounds like a good idea. It's also something i've been looking at a
bit. Take e.g. something like xchat. If you enable logging there you
basically keep your disc active all the time as xchat itself doesn't
use a large internal cache to write the data out every X MB or so.
And why should it, honestly? Bufffering data ist the OSes job 99% of
the time. As long as xchat does not use fsync() after each write we
should be good.
Maybe i wasn't clear enough. But take for example the difference between
xchat and say, syslog. I'd be really unhappy if i'd loose 1 hour of
syslog data in the event of a system crash, but i couldn't care less if
i'd loose 1 hour of xchatlogs during that time. So it is in that case
application specific in a way, and the kernel can't (and shouldn't)
semantically know how important your data is that you write with it. And
currently you can either do a write() and let the data be flushed to
disk automatically by the kernel every dirty_writeback_centisecs or
directly use a flush() after your write to make sure data is written
immediately. So the only way an application can currently "delay" those
writes is by using internal buffers that fill up and get written once
they are full. And the difference between 1 write every minute due to
dirty_writeback_centisecs and 1 write every hour because the buffer
takes that long to get filled is quite large imo.
Regards, Phil
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Philipp Knirsch | Tel.: +49-711-96437-470
Team Lead Core Services | Fax.: +49-711-96437-111
Red Hat GmbH | Email: Phil Knirsch <pknirsch@xxxxxxxxxx>
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Motd: You're only jealous cos the little penguins are talking to me.
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