[RndTbl] mysql crash and non-restart due to RAM?

Hartmut W Sager hwsager at marityme.net
Mon Jan 4 12:38:48 CST 2016

I am surprised.  Doesn't a current high-grade OS like Linux (maybe not
Windows) routinely close the gaps in RAM by relocating running code and
data?  This is quite efficiently do-able in CPU architectures that use
base/index/displacement memory addressing in the instruction set.  This was
introduced in the IBM 360 in 1964, carried forward into Intel x86, and
probably used everywhere else since then.

With base/index/displacement memory addressing, running code and data can
easily be relocated by copying it to the new location and changing the
contents of a few base registers, unlike the older architecture of entire
linear addresses stored in the instructions that would require the whole
program and data to have its addresses adjusted/rewritten after relocation.

(Yes, if this sounds "academic", I have an M.Sc. (1975) in computer
science.)  :)

Hartmut W Sager - Tel +1-204-339-8331

On 4 January 2016 at 11:32, Trevor Cordes <trevor at tecnopolis.ca> wrote:

> It looks like a ISP DNS blockage caused one of our ps's to fall behind
> on and have around 5900 little sub-ps's pile up.  Then a oom-killer
> triggered.  oom-killer is actually wonderful in this case as it logged
> the state of everything to disk.
> Jan  4 08:55:29 kernel: [5384435.328060] Node 0 DMA: 2*4kB 1*8kB 1*16kB
> 1*32kB 1*64kB 0*128kB 1*256kB 0*512kB 1*1024kB 1*2048kB 3*4096kB = 15744kB
> Jan  4 08:55:29 kernel: [5384435.329687] Node 0 DMA32: 14*4kB 43*8kB
> 62*16kB 35*32kB 7*64kB 16*128kB 67*256kB 21*512kB 2*1024kB 3*2048kB
> 20*4096kB = 123024kB
> Jan  4 08:55:29 kernel: [5384435.331315] Node 0 Normal: 15448*4kB 66*8kB
> 7*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB =
> 62432kB
> So it is fragmentation, or simple ram exhaustion, due to runaway small
> ps's due to blocked DNS.  Time to rejig the app to handle DNS going down.
> :-)
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