Re: LMB regression...

[Michael Ellerman <michael@ellerman.id.au>]

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On Wed, 2008-04-23 at 23:24 -0700, David Miller wrote:
> Paul, I finally got around to testing your changeset on sparc64, it
> breaks things:
> 
> commit d9024df02ffe74d723d97d552f86de3b34beb8cc
> Author: Paul Mackerras <paulus@samba.org>
> Date:   Sat Apr 12 15:20:59 2008 +1000
> 
>     [LMB] Restructure allocation loops to avoid unsigned underflow
>  ...    
> 
> Specifically, you removed the aligning of the size argument given to
> lmb_add_region() in the lmb allocators, and that is critical when
> allocating many small chunks, we run out of LMB slots otherwise
> and allocations start failing.
> 
> I added the alignment there as a bug fix earlier:
> 
> commit eea89e13a9c61d3928223d2f9bf2295e22e0efb6
> Author: David S. Miller <davem@davemloft.net>
> Date:   Wed Feb 13 16:57:09 2008 -0800
> 
>     [LMB]: Fix bug in __lmb_alloc_base().
>     
>     We need to check lmb_add_region() for errors, it can run out
>     of regions etc.
>     
>     Also, the size needs to be padded to the given alignment
>     or else the lmb.reserved regions don't get expanded and
>     instead we get tons of holes and eventually run out of
>     regions prematurely.
>     
>     Signed-off-by: David S. Miller <davem@davemloft.net>
> 
> Please be more careful in the future :-(
> 
> I find it quite ironic that you spent so much time and effort fixing
> an absolutely totally theoretical bug that nobody was triggering, and
> in the process reintroduced a real one that triggers immediately on
> real systems, and that had even been explicitly fixed previously.

Sounds like we need a test suite :)

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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