On Wed, 2006-Dec-13 10:50:21 -0500, Bill Moran wrote: >In response to Bill Moran <[EMAIL PROTECTED]>: >> sysctl kern.ipc.shmmax=2200000000 >> kern.ipc.shmmax: 2100000000 -> -2094967296 >> >> Looks like an unsigned 32-bit int. That doesn't seem to scale as well as >> would be expected on 64-bit arch (or PAE for that matter). >> >> Is this a mistake, or intentional? I'm working with some big memory >> systems, and I sure would like to allocate more than 2G for PostgreSQL >> to use ...
I thought POSIX specified 'int' but I may be mis-remembering. Tru64
uses int (and 2GB max) whilst Solaris allows 64-bit values.
Logically, shm_segsz and shm{min,max} should be intptr_t, shmall is
less clear but probably should be similar.
>int shmget(key_t, size_t, int);
>
>I appears as if those values should have been size_t all along. I'm
>_assuming_ that the return value is an identifier and not a memory
>address, which is what the docs seem to imply.
shmget() returns an "id" that uniquely refers to a shared memory
segment (stupidly designed SysV IPC namespace) and shmat() takes
the "id" and returns the address.
>So, my first thought is that all the int values in those structures
>should be changed to size_t. If I understand the use of that type
>correctly, it should always be the native word size on the architecture,
I believe intptr_t is more logical - an integer size that is the
same size as a pointer. Unfortunately, as I mentioned above, some
of this is specified in "standards" and logic is usually only present
by accident in such documents.
>but will that make this work for PAE as well, or should those be
>changed to uint64_t so they're 8 bits wide on all archs?
PAE is kernel only - userland still sees only 32 bits. (You can
fit more RAM into the box, but each process is still limited to
4GB - KVM size). Don't unnecessarily use [u]int64_t as it is
comparatively inefficient on 32-bit architectures.
I know Oracle (at least) avoids the problem on Tru64 by using
multiple SHM segments to allow SGA exceeding 2GB.
--
Peter Jeremy
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