Re: semtimedop instead of setitimer/semop/setitimer

Tom Lane wrote:

>Manfred Spraul <manfred@colorfullife.com> writes:
>  
>
>>... Initially I tried to increase MAX_ALIGNOF to 16, but 
>>the result didn't work:
>>    
>>
>
>You would need to do a full recompile and initdb to alter MAX_ALIGNOF.
>
I think I did that, but it still failed. 7.4cvs works, I'll ignore it.
MAX_ALIGNOF affects the on-disk format, correct? Then I agree that it's 
the wrong to change it.

>However, if you are wanting to raise it past about 8, that's probably
>not the way to go anyway; it would create padding wastage in too many
>places.  It would make more sense to allocate the buffers using a
>variant ShmemAlloc that could be told to align this particular object
>on an N-byte boundary.  Then it costs you no more than N bytes in the
>one place.
>
I agree, I'll write a patch.

>(BTW, I wonder whether there would be any win in allocating the buffers
>on a 4K or 8K page boundary... do any kernels use virtual memory mapping
>tricks to replace data copying in such cases?)
>
Linux doesn't. Page table games are considered as evil, because tlb 
flushing is expensive, especially on SMP.

--   Manfred