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Re: Problem with raidframe under NetBSD-3 and NetBSD-4

        Hello Greg.  I think I understand this e-mail.  However, I have a
question about changing the SusperReconUnit value.  Is there a way to do
this without unconfiguring the raid set and then reconfiguring it?  I can't
think of a way, but I thought I'd ask.

On Apr 6,  8:00pm, Greg Oster wrote:
} Subject: Re: Problem with raidframe under NetBSD-3 and NetBSD-4
} Brian Buhrow writes:
} >     Hello.  Following up on my own message, I can now say it's a memory
} > deadlock issue.  If I try removing the swap device from the system, wich is
} > the b partition of the raid set, and then issue the raidctl -F  component0
} > command to get the construction going, I get:
} > panic: malloc: out of space in kmem_map
} >     
} >     Since I assume it's a lot of work to change raidframe to use MALLOC,
} > and check to see if it failed, perhaps a reasonable work around, although
} > I'd prefer to see a real fix, is to note in the raidctl man page that users
} > who are swapping to raid sets may need to attach temporary swap devices to
} > their systems when attempting to reconstruct raid sets with large disks.
} > I'd also be happy with a kernel message saying that the allocation failed
} > and that the construction could not be completed due to a lack of memory.
} I think I've tracked this down.... 
} rf_reconstruct.c:rf_ContinueReconstructFailedDisk() is going suspend 
} IO's via rf_SuspendNewRequestsAndWait() and will call
} rf_reconutil.c:rf_MakeReconControl().  That, in turn, is going to call
} rf_reconmap.c:rf_MakeReconMap() which is going to do this:
} RF_Malloc(p->status, num_rus * sizeof(RF_ReconMapListElem_t *), 
}           (RF_ReconMapListElem_t **));
} For your array, it is going to be asking to malloc() something like:
}  1953524992 / 64 * 4 =~ 116MB
} which a) is just plain silly and b) that malloc() is willing to wait 
} for.  This, of course, causes your system to fairly quickly grind to 
} a halt since IOs have been stopped and the kernel isn't going to get 
} that much memory! :(  
} A workaround (untested) might be to bump up SUsPerRU (StripeUnits per 
} Reconstruction Units) to say 128...  That'd at least get the above
} malloc() down to a less-silly size... (As far as I know this should 
} work -- I believe I tested it many years ago, but I know I havn't 
} tested it in quite some time...)
} The fix is to re-work the reconstruction code so that it doesn't need
} to preallocate so much space... that's going to be a major undertaking, 
} but one that appears to be necessary :( :(  
} Later...
} Greg Oster
>-- End of excerpt from Greg Oster

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