Re: Linux memory handling improvement

Neil Conway wrote:

>On Mon, 2003-09-15 at 07:32, Andrew Dunstan wrote:
>
>
>>This will probably take a while to make its way into vendor kernels, and
>>even then we'll need to keep the warnings in the docs for people running
>>older kernels. I am not sure at this stage what its status is for the 2.6
>>kernel series.
>>
>>
>
>The 2.6 kernel series uses a VM written by someone else (Rik van Riel),
>so I don't think that 2.4 VM improvements are relevant to it. But it's
>definitely a good thing that the -AA VM improvements are finally being
>merged into the mainline 2.4 kernel.
>
>

Really? I haven't been following that closely. I thought it was
basically the Arcangeli VM with the van Riel rmap stuff. Anyway, Joseph
Pranovich's "Wonderful World of Linux 2.6 says this:

There is one further stability issue that has been resolved with Linux
2.6: it is no longer possible to allocate more than the maximum amount
of RAM (plus swap) you have on a system. Previously, Linux would allow
the malloc() ("memory allocation") system call to succeed in some cases,
even when memory is exhausted. The overcommitment logic has been revised
and this case should now be impossible. (Of course, if you run out of
RAM on the system-- even without exceeding the maximum-- you have worse
problems to worry about.)

(see http://kniggit.net/wwol26.html )

So from a PostgreSQL p.o.v. we should be in good shape with any luck.

However, doing a little more reading I'm not quite as confident as I was
that we are getting an improvement in 2.4. See
http://kerneltrap.org/node/view/805

cheers

andrew