Memory Problem

[Nicolas Michel <nicolas.michel@xxxxxxxxx>]

Hi here,

Our server had 2GB of RAM. We added some memory to have 16GB. We are on a debian etch. I installed the "bigmem" kernel to use the all memory :
>     ~# cat /proc/meminfo 
>     MemTotal:     16573232 kB
>     MemFree:      15448836 kB
>     Buffers:        133772 kB
>     Cached:         445388 kB
>     SwapCached:          0 kB
>     Active:         782764 kB
>     Inactive:       302760 kB
>     HighTotal:    15794120 kB
>     HighFree:     14838384 kB
>     LowTotal:       779112 kB
>     LowFree:        610452 kB
>     SwapTotal:     2658716 kB
>     SwapFree:      2658716 kB
>     Dirty:             452 kB
>     Writeback:           4 kB
>     AnonPages:      506336 kB
>     Mapped:         126524 kB
>     Slab:            27620 kB
>     PageTables:       3036 kB
>     NFS_Unstable:        0 kB
>     Bounce:              0 kB
>     CommitLimit:  10945332 kB
>     Committed_AS:  2187952 kB
>     VmallocTotal:   118776 kB
>     VmallocUsed:      3716 kB
>     VmallocChunk:   114640 kB

I wanted to give to postgres 4GB. So I tryied to set shmmax to 4Go :
>     sysctl kernel.shmmax=4294967296

But it doesn't work : if I launch after this modification this command :
>     sysctl kernel.shmmax
it gives me this response :
>     kernel.shmmax = 0
>     
Why? Is there a limit to shmmax?