Re: dynamically allocating chunks from shared memory

Excerpts from Robert Haas's message of lun jul 26 08:52:46 -0400 2010:

> Here's another idea. Instead of making imessages use an SLRU, how
> about having it steal pages from shared_buffers? This would require
> segmenting messages into small enough chunks that they'd fit, but the
> nice part is that it would avoid the need to have a completely
> separate shared memory arena. Ideally, we'd make the infrastructure
> general enough that things like SLRU could use it also; and get rid of
> or reduce in size some of the special-purpose chunks we're now
> allocating.

What's the problem you see with "another shared memory arena"? Right
now we allocate a single large arena, and the lot of shared_buffers,
SLRU pools, locking objects, etc are all allocated from there. If we
want another 2 MB for "dynamic shmem", we'd just allocate 2 MB more in
that large arena and give those to this new code.