> Hi all,
>
> In the kernel include file include/asm/shmparam.h SHMMAX is set to
> 16MB (0x1000000) and I was wondering if it would be a bad thing to
> set it to 64MB (0x4000000) or 128MB (0x8000000) provided the machine
> in question had 64MB+ or 128MB+ memory.
In theory, increasing SHMMAX to 128MB should be possible... Beyond that,
not without difficulty - the mm subsystem uses 128MB swap areas, of which
shared memory is one.
> The purpose is I've implemented my own database and it needs to share
> large amounts of memory; 64MB may not be enough but it'd be a good
> start. The ideal machine for this database would have 128MB+ which my
> test machine has and to keep the data off the disk once loaded.
Another alternative that will work with both 2.0.x and the future is to
use shared mmap()ing of a file - that way you don't need to rely on users
to tweak their kernel. Making use of the mmap()ed region to perform i/o
could also net you a performance win...
-ben