On Dec 29, 11:13 am, Volker Braun <[email protected]> wrote:
> We set up GAP to reserve a lot of swap on systems with a lot of free swap.
> 640kb is not enough for everybody.

Agreed. It sucks that GAP needs an upper limit at startup, but we
won't be changing that.

I retract my complaint about sage not starting up: The gap allocation
is in a separate process, so it can't possibly affect sage startup! In
principle it could mean that gap initially tries to allocate too large
a swap area, but I think gap adjusts for that by itself. It would be
cleaner to take user limits into account, of course.

For a longer term solution: It's clear that on a machine with more
memory you'd probably want a larger chunk of memory by default.
However, on a machine with A LOT of memory, it's likely that you'd
like to run more processes in parallel, so you probably want to
allocate a smaller percentage of total memory. So perhaps the
heuristic should take something proportional to the sqrt of available
memory (properly weighed depending on whether this is determined by
swap or physical memory), capped above by a fixed percentage of a
memory limit and capped below by a fixed minimum required to run
doctests.

You can of course bicker about what the exact exponent should be :-).

Is this issue going to haunt us for libgap as well? There it's a lot
more serious, since then the gap allocation really is at the expense
of the rest of sage, within set quota.

Note that setting limits is a very sensible thing to do nowadays. Most
of the time, excessive memory use is due to a bug. It's much better to
catch that early, when memory footprint has grown to only 2Gb, than
later at 16Gb, when all other processes on the machine start to get
affected as well. So we should ensure that Sage works well with set
limits.

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