Re: ReiserFS / 2.4.6 / Data Corruption

From: Hans Reiser (
Date: Mon Jul 30 2001 - 18:12:38 EST

Rik van Riel wrote:

> > If you could halve linux memory manager performance and check as
> > many things as reiserfs checks, would you do it.
> I haven't removed a single debugging check from the
> 2.4 VM. Performance is MUCH more reliant on things
> like evicting the right page from RAM or reading in
> the right page at the right time.
> CPU usage is only secondary.
> > .. You made the right choice.
> Thanks ;) [yeah, yeah ... flame me about out-of-context]
> > Now, if you add a #define, you can check as many things as
> > ReiserFS checks, and still go just as fast....
> I'm sure these checks make reiserfs a tad more CPU hungry,
> but isn't the real win in reiserfs supposed to come from
> superior disk layout, readahead across files, etc... ?
> Or is that all just a myth ?
> regards,
> Rik
> --
> Executive summary of a recent Microsoft press release:
> "we are concerned about the GNU General Public License (GPL)"

A tree is a complex structure. You can check it, and the temporary structures
involved in balancing it, quite a lot of ways while balancing it. I believe you
that the checks you need for your code have no significant performance impact.
Ours sometimes do. Consistency checks can be quite a bit more than a tad
consumptive of CPU. Like I said, there were a few checks we removed after the
bug was gone because we got tired waiting for our debugging iterations taking so
long because of them.

Using the #define means we don't have to think about the effect on performance
of a check, we just leave it in. Some checks belong outside the #define
(checking to see if garbage came back from disk is left outside the define
nowadays.) Distros should trust the developers in these tradeoff decisions.
Otherwise, things just get stupid.

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This archive was generated by hypermail 2b29 : Tue Jul 31 2001 - 21:00:47 EST