[Dovecot] severe performance problem (mail cache related?)

Dan Price dp at eng.sun.com
Fri Feb 16 11:29:09 UTC 2007

On Fri 16 Feb 2007 at 01:12PM, Timo Sirainen wrote:
> On Fri, 2007-02-16 at 03:05 -0800, Dan Price wrote:
> > On Fri 16 Feb 2007 at 02:49AM, Dan Price wrote:
> > > > So.. Hmm. Could the problem simply be that the mmap-copy-growing is too
> > > > slow? If the user really has some 25MB cache file, that could be it. I
> > > > think I could change the code so that it mmap()s immediately enough
> > > > memory to fit the whole cache file. Probably a good idea to do anyway.
> > 
> > One thing I don't totally get is why you mmap anon here, if this is
> > really about a cache file?  It seems that you could mmap the cache file
> > directly, perhaps with MAP_PRIVATE if you need to make in-memory-only
> > changes.
> Yes, and it's done as long as you don't have mmap_disable=yes. Hmm.
> Weren't you using ZFS directly? Why are you using mmap_disable=yes? :)
> Its main purpose is to make indexes work in NFS.

Well there you go, I'm a dope.  I think I set mmap_disable=yes because I
was seeing strange things happening where there would be thousands
(millions?) of madvise(DONTNEED) calls-- seemingly forever in a loop.  I
have not yet tracked that problem down-- next time I see it, I will
make sure to get to the bottom of it.

I must have decided that turning off mmap would also halt the advice...
who knows, it has been a rough week.  There's a lesson: know what the
hell you are doing before changing settings :)

I will run tomorrow with mmap_disable=no and see how it goes.


Daniel Price - Solaris Kernel Engineering - dp at eng.sun.com - blogs.sun.com/dp

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